Omori Thoughts

3-pronged shadow figure appearances (updated throughout the game):
- North of the Home Stump, at the pier where Omori fears drowning
- [REAL] Home, at the bathroom door through the mirror, after opening the door for Mari
- At the center of Basil's house, right before Omori's party enters, for the first time after they realize Basil is missing
- Vast Forest, in a tire swing
- [REAL] Basil's bathroom, in place of Basil when looking through the mirror
- [REAL] Sunny's house, when it is filled with spiders
- Pyrefly Forest, at a tree stump before Shadow Basil leads you to the Lost Forest
- Across the vines in the entrance to Sweetheart's courtyard
- [REAL] Home, at the bathroom door through the mirror again, but this time after seeing Mari in Mom's room
- At the island in the lake in Otherworld; this layout of the lake and island seems to resemble the lake in the hangout spot in the real world.

Shadow Basil appearances (updated throughout the game):
- Old Bridge, in the same platform as the R key, currently inaccessible
- Otherworld entrance, after beating Space Boyfriend, leading you to the forest and then the barn and into the giant picture frame
- Pyrefly Forest, leading you to the Lost Forest
- Water, north of the home stump, many appearances while swimming alongside Mari

GENERAL THOUGHTS AND THEORIES

---

After acquiring Special Mixtape for Space Boyfriend

So it seems this entire world is Omori's dream, including the white space and all, with the real world being the house where Omori woke up hungry at night with messages from Mom. He is dreaming about going on this adventures with his friends.

The whole sequence of walking down the stairs endlessly with all the creepy hands was all in Omori's imagination, arising from his fear of heights. He was eventually able to overcome it through a voice in his head (which I am guessing is Basil), allowing him to CALM DOWN. Still though, it's quite odd that his fear prevented him from even walking down the stairs of his own home, even if he's alone and it's dark. I am guessing that the fear of heights arose from a recent traumatic experience that he still hasn't recovered from.

The dream world also has two places highlighting Omori's fear of drowning and spiders respectively. I am guessing those are also fears that he will need to overcome later, and those fears might also have spawned from notable traumatic experiences.

The reason why the steak was bad was likely because there was no electricity, so the refrigerator did not preserve it. The microwave seemed to be working, with the signature chime and all, but Omori may have imagined that. Even if the electricity did return by then, it was likely gone for several hours before, so the steak would go bad regardless.

Mari seems to be Omori's older sister, based on how she said she was returning home when she knocked on the door in the real world. But there was a blue ghost figure of sorts (even haunted him in the bathroom reflection), so maybe Mari did not actually return home, and Omori just imagined her coming back during this difficult time of moving out.

Hero and Mari seem to be married, based on their interactions in the dream world. That would explain why Mari in the real world is not living with Omori. Hero and Mari probably live far away, so Omori doesn't seem them often.

Now for Basil: my guess is that he is a close friend of Omori who died. Omori might have witnessed the death, so it would have been especially traumatic, and the event itself may have led to Omori developing one or more of these three fears he has now (heights, drowning, spiders). Omori has been dreaming about doing stuff with Basil, but his subconsciousness is starting to acknowledge that Basil is no longer with them, which is why he disappears in the dream world. One of the photos (that is only shown to us too briefly to make out any details) seems to be an indicator of Basil's death (maybe he took the photo right before he died, and whatever it captured is a strong reminder of that traumatic event, so seeing this picture caused Omori's subconsciousness to erase Basil from the dream world. However, Omori is still in denial of Basil's death, likely as a coping mechanism, so he and his friends in the dream world start looking earnestly for Basil as if he should be here.

---

THREE DAYS LEFT, after Sunny goes to sleep, and Omori meets up with Mari and the others

Man, the whole Shadow Basil sequence at the Outerworld forest made me even more confident in my dead Basil theory, only for the real world to disprove it by showing Basil in the flesh. There are still disturbing factors surrounding Basil, but it does seem he is very much alive in the real world. Instead, Mari is the one who actually died. This better explains the blue ghost from Omori opening the door to Mari in the previous night (with the knocking and Mari's voice being hallucinations).

Aubrey says Sunny hasn't left the house in 3-4 years, so that must have been when Mari died, with Sunny still traumatized by it. Kel explained about Hero's struggles to recover, which suggests a close relationship, though it seems they did not get married just yet. Aubrey struggled a lot, and closed off her friends who failed to support due to their own struggles with recovering from Mari's death, leading Aubrey to eventually become this pink-haired biker punk with a baseball bat.

So what's the deal with Basil then? Why is Sunny seeing the shadow figure in the real world, albeit only in a mirror reflection? Here is my theory: whatever the incident was that caused Mari to die, it was one for which she died to save Basil, at least from Sunny's perspective, so Basil could have been the one to die instead of Mari. Sunny subconsciously seems to blame Basil for Mari's death, possibly wishing that Basil was the one to die instead.

At the beginning of the game, he was still dreaming that both Basil and Mari were alive and well, and the six of them would play together happily. But the picture triggered Sunny's subconsciousness into accepting the reality that Mari and Basil cannot both be alive. This is when Sunny woke up last time, hungry. He overcame his fear of heights by imagining Mari's voice (not Basil's), and he later imagined Mari knocking on the front door. By the time he returned to sleep, his subconsciousness was adamant about preferring Mari's survival over Basil's (in denial of the reality), so the dream world erased Basil while Mari is still with them, interacting with them in the same manner as usual.

I'm also starting to notice that the dream may also be switching the two in some other contexts as well. For example, Aubrey said Basil used to brush her hair, which is... very odd and it is likely Mari that brushed her hair instead. But this line likely came from an actual statement that Aubrey said in the real world when missing Mari, but Sunny's subconsciousness switched Mari with Basil when recounting it in a dream because Basil is the one who should be gone. Same applies to Kel recalling Basil telling him to brush his teeth. Friends of the same age wouldn't do that, but Mari seems to be an onee-chan for the whole group (except her fiance Hero), not just Sunny.

As for the 3-pronged shadow, it seems Sunny sees that in place of Basil. This is especially disturbing when it happens in the real world, with Sunny being so emotionally distraught that he perceives this 3-pronged shadow in place of Basil when seeing him reflected in the mirror.

As for what this 3-pronged shadow actually is, I can only speculate:
1) maybe this figure represents a reaper, with Sunny perceiving Basil as a murderer for "killing" Mari.
2) maybe it represents an empty void, reflecting Sunny's refusal to acknowledge Basil's presence, desperately seeking a world where Mari takes his place.
3) maybe the shape represents something Sunny specifically saw relating to Mari's death. For example, if she died from drowning, maybe the 3-pronged figure is the shape he saw in the water after she was submerged. Basil's existence reminds Sunny of that chilling memory.

The second and third ideas wouldn't explain the eye, but maybe the eye represents life, suggesting that this shape is so prominent in Sunny's perceptions that it feels alive, even having its own eye.

Sunny's general behavior is also disturbing, despite the player making such choices. He apparently shut himself off for 3-4 years, but when he finally stepped out, he brought a steak knife with him. He drew this knife against Aubrey of all people, who used to be one of his closest friends and is implied to have had a crush on him back then. He barges into the church to confront Aubrey, despite Kel insisting to wait until the sermon, though I don't think Sunny intended to provoke Aubrey into making such a scene. When Basil is distressed in the bathroom, Sunny just walks away without even any words of comfort. While the player would probably freak out on seeing the 3-pronged shadow, Sunny's perspective might not necessarily be the same, and his own reflection was completely expressionless, as always. Even in gameplay, Sunny never has any emotions in the real world, except being afraid and that's only when confronting his fears in the privacy of his own home.

This might sound crazy, but I think Sunny might even try to kill Basil at some point in the future.

Basil's behavior is quite consistent with the idea that Mari died to save him. He probably also blames himself for her death. His four friends all had a hard time recovering as well, so they weren't comforting Basil to reassure him that it wasn't her fault. Even Hero, the aniki figure, apparently didn't go outside for a year. Basil's parents are always traveling around, so I am not sure they were able to give Basil the emotional support he really needed.

Not only does Basil blame himself for Mari's death, but I think he also suspects that Sunny also blames him for Mari's death as well (which I also think is a correct deduction). But Sunny refused to come out of his house for 3-4 years. I expect Basil knocked on the door many times in the hopes of reconciling with Sunny, or just to speak out his emotions, but Sunny never opened the door, preventing Basil from getting even a single word through. Basil may be prepared regardless of whether Sunny forgives him or hates him, but not knowing Sunny's feelings on the matter is driving him crazy. Sunny finally came out, but in a completely silent and expressionless state, saying nothing, so Basil still cannot get closure. When Kel reveals that Sunny is moving out in 3 days, Basil loses it because his agony of not knowing Sunny's perspective on this may never be resolved. Sunny visits him in the bathroom, but instead of comforting or even just speaking out a single word, he just looks at the mirror and leaves Basil alone.

This might not sound as crazy, but I think Basil might try to kill himself at some point in the future.

Questions that AbdullahTrees asked me to address:
1) Three days left? What happens after three days?
2) Who is omori?
3) Where is Mari?
4) How did Mari "die"?
5) Why was the steak spoiled?

My current answers
1) Sunny moves out after three days. But what's probably more significant is that Basil might try to kill himself once there are no more opportunities to connect with Sunny. Or, less likely, Sunny might even try to kill Basil in his deranged state of denial over Mari's death.
2) Omori is Sunny in the dream world. Not sure why the name is different, while his friends retain their irl names. Maybe it's a name he made up for himself, because he doesn't like Sunny, or because he wants to imagine himself as a different person in the dream world (despite having the same friends).
3) Mari should be resting at the gravestone in the cemetary? The fact that you asked this suggests that this is a significant question (spoiler!), and now I am wondering if her body was actually never recovered.
4) I don't know the details, but I suspect it relates to one (or even all) of Sunny's three big fears and that she died to save Basil, so Basil could have died in her place while she lived on instead (at least from Sunny's perspective). For example, maybe the six friends were having fun on top of a high cliff overseeing a lake or sea when some spiders crept up, panicking Basil and causing him to almost fall off the cliff, but Mari quickly grabbed him and saved him, but lost her own footing in turn, and she ended up falling off the cliff, plunging into the water. Sunny witnessed the entire event, subconsciously blames Basil for Mari's death, and the vision of the dark silhouette of Mari's body submerged in the water was imprinted into his mind as this 3-pronged shadow that haunts him to this day, to the extent that it now feels alive, gaining a creepy vertical eye.
5) Mom said the electricity was cut off a few days earlier than the move-out date due to a misunderstanding of when they were moving out, so the refrigerator was not preserving the steak.

---

After hearing the story about a DREAMER in the lost forest

I think it's pretty apparent that the DREAMER is Sunny/Omori. Originally, it was just Sunny and the white room in the dream. After Mari died, Sunny refused to come outside his house irl and interact with anybody except his Mom. But in his dreams, he eventually made a door that opened up to other worlds, and he conjured up Mari and his friends, going around these various worlds with these friends. Of course, as these are entirely dreams, all of the details are generated from his own subconsciousness. Indulging in these dreams is how he coped with losing Mari irl, while she is alive and well in his dreams.

However, he could not maintain this state of denial over Mari's death forever. He subconsciously knew that Mari was dead, and I suspect he specifically witnessed her demise as well, a deeply traumatic memory that he tried to seal off. Despite his attempts to suppress it and forget about it, this darkness in his subconsciousness manifested in his dream world. I am not sure if there is a particular area in the dream world that is referred to here, maybe the black world inside the picture frame that Shadow Basil guided me into? Once he entered that area (in his dream), he recalled the trauma from Mari's death. Mari's death continued to haunt him in his dreams, even after fleeing that world of darkness.

The story says he conjured up benevolent entities, this may be referring to his friends (including Mari)? I guess that would suggest that they weren't there until after he entered the world of darkness for the first time? He build more worlds, sealed off any paths to that dark world, but it still plagued his mind.

> What the DREAMER had created was something he could not be a part of, something outside himself

I think this is indicating that while Sunny could manipulate and create more worlds in his dream, the darkness that manifested in his subconsciousness is something that he could not manipulate or erase, no matter what kinds of changes he makes in the dream world, as this darkness is from his own self, his own subconsciousness.

> The DREAMER's own power was his greatest adversary. Knowledge... or the absence of it, would become the DREAMER's greatest gift

His own knowledge and imagination is what constructed all these worlds, but that knowledge included his memories of Mari's death, a darkness that that haunted him as his greatest adversary. His greatest gift, i.e., his coping mechanism against the trauma, is to try to forget about the incident and Mari's death, so that this darkness is absent in his knowledge. He changed his name from Sunny to Omori in the dream world, so that he could subsconsciously think of him as a different person, which would help him forget the dark memories.

> From that time on, the DREAMER has lived amongst us... simply as an inhabitant of this world... Traveling along blissfully, ignorant of his own fabrication

The player who plays the game represents Omori, which is a state of Sunny that tried to forget everything in the past. The player starts the game with no memories of Sunny's past. They wander around these worlds, not knowing their origins, blissfully ignorant of the reality.

> Though the DREAMER may have subdued the inexorable, the darkness grows still.
> No bandage can stifle an eternal wound... and there will be a time when its influence will bleed through.
> Forgetful the DREAMER may be of this peril, a peril never forgets to be.

Despite Sunny's attempts to forget about the dark past, the darkness itself still exists within his subconsciousness. The reality of the events cannot be undone. It will eventually resurface no matter how much he tries to suppress it.

> Yet, the end of this world may be an inevitability. The DREAMER is the only one with the ability that can truly set this world free.

This state of blissful ignorance that supports such fantasy worlds will inevitably end. Sunny cannot completely erase the darkness from his mind. As for setting the world free, I think the ability here is for Sunny to confront the darkness in a healthy manner, accepting the reality of Mari's death, moving on from it, and working towards a productive future in the real world, which would in turn, brighten up his dreams as well without the darkness plaguing it.

That was the end of the story, but I also want to add that I think Omori represents the perspective of the player who is playing the game. They play the game after Sunny tries to forget about his past, creating the Omori persona that has no memories, just like the player who starts playing the game with no knowledge of the past. I believe this also extends to Sunny in the real world, who is now in a state that does not consciously recall anything of the past.

However, the past still persists in his subconsciousness, which affects the dreams and also affects his perceptions in the real world.

Anyway, with this perspective, I no longer think Sunny has any dangerous ideas like wanting to kill Basil, because I think his current state really does reflect that of the player. He pulled out a knife against Aubrey because he was accustomed to the JRPG gameplay in the dream world, just like the player playing the game, and not for any deeper sinister reasons.

I do still think Basil wants to kill himself though. Sunny tried to patch up his trauma by forcing himself to forget the past (which is obviously not a permanent solution). But Basil not only remembers everything, he likely was not able to cope with his trauma in any healthy manner at all.

TWO DAYS LEFT, before going back to sleep

The books inside the dim library (that you fall into after beating Sweetheart) seem to have stories from the past of the main characters. Names are hidden, but their lengths aren't, so we can generally figure out who is who. Sunny seems to be represented by one letter only though. I suspect the Doylist reason behind this is that players can name Sunny with any length, which would affect how well they can identify the names here. But there should be a proper Watsonian explanation as well; my guess is that once Sunny transformed into Omori (to disassociate himself from his dark memories), the name Sunny was blotted out from the dream world, to the extent that any records of it are shown as a single blank character of sorts, which is why this name appears as length 1 in the books.

One of the books recounts a story of Kel and Hero taking turns in jumping off a tall statue over a lake. They convinced Sunny to try it out, but then a spider crept up when Sunny was at the top, scaring him into falling down. This single incident does explain Sunny's phobias of heights, spiders, and drowning. But what bothers me is that it does not seem to relate to Mari's death at all. Is this event truly unrelated to Mari's death? Or was Mari's death associated with this incident somehow, e.g., maybe she died while trying to save him? I'm still convinced that Sunny perceives Basil as connected to Mari's death, so this does suggest that her death is not related to the incident of Sunny falling into the lake.

There are some other notable parts to the books that stood out to me:

> He makes a vow to himself, that no matter what, he will remember this moment forever

It's just a happy memory of dozing off in the car, but I think Sunny did forget this memory, once he prioritized indulging in his dreams as Omori.

> over an hour has passed since [Mari] has climbed down her ladder

This may seem unremarkable, but... Sunny noted this, at least subconsciously (I assume there are no actual books in the real world with these stories), and to add to that, this is a game where the writing consciously included such phrasing, so I am convinced that this is significant. Was Mari held up by something after she climbed down her ladder? Maybe the other friends went to check on her and something notable happened? Like... her death? Anyway, I'm noting here that the context is that the friends were building a treehouse on a hot summer day (the "hottest", according to Sunny).

> what he thought would be a rewarding hobby has been nothing more than a nuisance

Sunny seems to be losing interest in the violin, primarily because it cuts into his time having fun with his friends. This makes me think his violin lessons are pushed by his parents (probably just his mom; his dad has been out of the picture at some point, but I'm not sure when and why). In fact, I would guess that his parents (or just his mom) is quite strict about Sunny keeping up with his studies in general, probably allowing him very little free time, which leads Sunny to daydream about these fantastical adventures during his classes and such.

Also, the mention of a violin reminded me of some stuff that has been on my mind a while back, but I didn't think too hard about them nor did I actually write them down. Back when Omori was pursuing Shadow Basil in the Otherworld, one of the memories was about how his friends (or I presume are his friends) pooled together to get one big gift. Several gift boxes were shown, but one of them was particularly shaped like a violin. Back then, I thought these were Basil's memories, but now it seems they were actually Sunny's.

The photo album adds more clues, but there are still some holes. Sunny was learning to play the violin so that he could participate in Mari's recitals. Did he not enjoy doing so? Or maybe he initially wanted to be involved, but once he actually started the lessons, and it cut into his time with friends, he no longer wanted to do it anymore, but his parents (or just his mom) pressured him to continue his lessons regardless?

A photo album caption also said that his friends pooled together to get one big gift, exactly like the Otherworld memory said. However, this caption said the gift was "building blocks", which certainly doesn't sound like a violin. I wasn't sure what building blocks meant back then, but now I suspect they were components to the treehouse that the friends started to build. The treehouse being a gift to Sunny would also explains why Sunny was able to get away with slacking off at all while his friends worked hard.

But if the gift that his friends pooled together for was a treehouse, then what about the violin? Why was the violin present shown in the memory while pursuing Shadow Basil, with roughly the same dialogue about his friends pooling together for a big gift? Was the violin an earlier gift that the friends also pooled together for? My current guess is that the violin actually a gift from someone else (like his mom), and it was shown in the memory because it was the same birthday where he got the treehouse (the memory did have other cubic gift boxes iirc).

As for why the violin is significant to begin with, I think the violin reminds Sunny of Mari, because he started playing it in order to participate in Mari's recitals. After Mari's death, the violin would awaken his past trauma. I am guessing the violin is currently hidden inside his closet.

Speaking of the closet, let's get into Sunny's house now. I originally thought the glass doors at the living room were to his closet, but Kel/Hero indicated that it leads to the treehouse instead (presumably Sunny's backyard). More importantly, when approaching the stairs, Kel/Hero mentioned that they remembered the hallway with the closet to the left and the piano to the right. This confirms that the mysterious door on the left that was shown when Sunny confronted his spider fear is the door to the closet. But that door is not shown right now.

I originally had two theories about this door: either the door was sealed up, possibly to help Sunny feel comfortable in his own home without dealing with the trauma associated with whatever lay behind the door (I thought it was the door to Mari's room), or the door is still there, but Sunny doesn't perceive it because his subconsciousness blots it out, causing him to "see" the wall continuing through it with no door. With Kel/Hero bringing up their memories of the closet, this rules out the former possibility, since they would have mentioned that the closet isn't there anymore or at least some indication that the current state is different from how they remembered it. Furthermore, one of Mom's notes was to clean out the closet, so Mom at least thinks the closet to be accessible to Sunny, i.e., it's not physically sealed off. Ultimately, these details confirm that the closet is actually still there, with the door and all, but Sunny just doesn't see it there for some reason. Examining it gives the response that "there is nothing here". Sunny's subconsciousness refuses to acknowledge the closet, and it is hidden from his perception. The earlier appearance of the 3-pronged shadow figure in the mirror of Basil's bathroom already suggested that we are seeing is still a reflection of Sunny's perception, even when we are in the "real world", as opposed to depicting the physical reality.

Anyway, this leads to the question of: why is the closet so especially traumatic to Sunny, to the extent that his subconsciousness erased it from his subjective vision? Is it simply because it contains some of Mari's belongings? That doesn't justify such a strong reaction. The violin may be in there, but Sunny can see pictures of himself playing the violin and hear his friends talk about the violin, so it can't be that bad (but I do still think the violin is somehow connected to his trauma). This psychological rejection implies something far more sinister about the closet. Like if he was locked up in the closet for several hours, desperately trying to get out, completely terrified, but he then witnessed Mari getting brutally murdered while peeking out through a small opening. I know, that's a really contrived scenario that is unlikely to have happened, but that's the kind of event that I expect could have happened to justify Sunny reacting like this to the closet.

And then there's the piano. When I saw the piano in the church, I already felt that it looked a bit ominous, and the shape kinda resembled the 3-pronged shadow figure. But now that we find the piano inside a room that Sunny refused to enter previously, it suddenly became a lot more significant. That being said, it's not as severe as the situation with the closet, so it's possible that the piano's significance is only that it reminds Sunny of Mari. There are two things in the piano room that stood out, however. One was the very large curtain behind the piano. Maybe the curtain was hiding a big window, but... that seems too big for a window, and I visited many other houses in this neighborhood without finding any of them with such a large window / curtain. I feel like the curtain is being used to cover... something else. Like, maybe there is a big framed picture behind it? A picture of Mari? A picture of the whole family, but it was covered up because the father was in it as well? I am not sure, but I don't think there are much hints at this point.

The other feature that stood out is the etching of OMORI in the piano. AFAIK this is the first time the name Omori shows up in the real world. I was wondering if it was the name of a piece, but that would not have been etched into the piano itself. Is it the name of a person? This is the piano that Mari played, so shouldn't she have written her own name in it? The piano was played by Mari, but the name Omori is used to represent Sunny in the dream world, so I expect the name Omori is connected to both Sunny and Mari somehow, as opposed to being limited to one or the other. Is Omori the name of their father, who originally owned the piano that Mari inherited? We don't actually know anybody's last names, so could it be they are the Omori family? I can see a child being named Sunny Omori, but Mari Omori is a little odd. Unlike the curtain but like the closet, I am very sure the name Omori is extremely significant, but I still can't find a compelling explanation.

Regarding the whole incident at the lake, this seems to further support the idea that Basil is associated with Mari's death. In fact, it seems it is not just Sunny who blames Basil for Mari's death, but Aubrey does so as well. I would not be surprised if Aubrey would also see Basil as a scary shadow figure if she were to gaze at his reflection. Also, from a meta perspective, the fact that this game still hasn't hinted about any of the circumstances around Mari's death except for Basil's connection to it, which is emphasized even further, makes me think that her death is actually a lot more disturbing than what I imagined. It probably isn't just an accident of her falling into the water, but something a lot more brutal. I don't think she was murdered though, since the character's behaviors suggest that nobody was responsible for it more than Basil, but they seem to acknowledge that Basil had no malicious intentions whatsoever. Whatever blunder it was that he made, it must have led to a really nasty gruesome incident that not only killed Mari, but heavily scarred all five of her friends, to the extent that at least three (Sunny, Aubrey, Basil) out of five of them still haven't fully recovered 3-4 years later. Kel may not have been a direct witness to the incident, because he seems surprisingly stable emotionally compared to everyone else, though part of it may be due to the forced responsibility of having to help his brother, who had it much worse (as it was his wife/fiancee who died).

That being said, there are also further hints that the incident happened at the lake, near their hangout spout. In particular, the area seemed to have been cordoned off, for which the most likely explanation is that it was blocked off due to this incident, further suggesting that it was probably a really shocking event. Upon examining the lake, Sunny recalls that his fell in once, with water in his head for weeks... and it sometimes feels like some of it is still there. This is obviously not referring to literal physical water, but seems to be implying that he hasn't fully recovered mentally from that event. That being said, despite these hints about the lake relating to Mari's death, Sunny's reaction to the lake is nowhere near as severe as his psychological rejection of his closet, so I am guessing that whatever is in the closet is a lot more disturbing than the lake itself, implying that Mari did not simply die from drowning. It is also possible that, just as Sunny does not perceive the closet anymore, there may be some features around the lake that Sunny is also subconsciously blocking out, so we don't get to see them either.

Another reason why Mari likely did not die from drowning is how Sunny overcame his own fear of drowning. Like the previous two fears, it was his memory of Mari that saved him, hearing her voice inside his head. But unlike the previous two fears, this time he explicitly has a memory of Mari swimming underwater to save him. While the actual event may have been exaggerated in his mind, it does suggest that it was Mari who rescued him back when Sunny fell into the water, and it would not make sense for his mind to still see Mari as a light shining against this fear of drowning if Mari herself actually succumbed to a watery grave. So while I do still think that her death is associated with the lake somehow, I am pretty sure she did not die from drowning herself.

---

AFTER HUMPHREY (before approaching Basil's house)

First, I wanna think about why this dream begins at the friends' room (instead of WhiteSpace) with everyone missing. Yes, they are later shown to be working for Jawsum and all, but that's simply the headspace justification for the scenario, whereas the actual reason for the events turning out this way is likely related to Sunny's psychological state. I thought at first that it may have something to do with Kel and Hero sleeping in the same room, but couldn't come up with a proper explanation in that direction, so now I think it's more related to Omori coming closer to the darkness, as indicated by the progress towards the hangman. As Daddy Longlegs said, the Dreamer manifested "benevolent entities" due to this darkness, so my guess is that Omori was drawn to the darkness when the dream started, but he was afraid to confront it alone, when the Mari (in his mind) guided him to his friends to comfort him. In fact, maybe the comforting presence of Kel and Hero sleeping in the same room is what allowed Omori to actually find Kel and the others eventually, as opposed to being left entirely by himself (and maybe Mari).

We see the big curtain again, and it's where this Mari disappears. She changes to a black-and-white form for some reason and wishes goodbye, suggesting that this Mari is different from the usual Mari we find in the picnics (who continues to show up after this). Behind the big curtain is actually a large window after all, and not a picture of some kind, but I am not sure why it's so significant. It's the window behind the piano, so maybe it's where she would watch the others play with each other while she plays with the piano? I am not sure what the goodbye is... maybe because this is the last time (in this "cycle") where Mari plays an active role in helping Sunny instead of returning to being like an NPC, simply sitting in one spot, talking and hosting picnics?

The idea of a repeating cycle was implied in the portal left by Humphrey. In each cycle, "the path to the truth" (entrance to Black Space?) is hidden in some location, but the flower boy (Basil) always finds it and Mari always guides Omori to it. In this case, the portal is at Basil's house, and Mari pushes Omori and the others to search for Basil, towards these various areas with various hangman keys that will unlock the portal to Black Space.

While the "path to the truth" is currently in the heart of a vast forest (Basil's house), it used to previously (earlier cycles) be in the portal that Humphrey left behind -> lighthouse in a pier -> library banished deep underground -> an old barn in a distant planet. I don't remember seeing a "lighthouse in a pier", but the old barn in a distant planet likely refers to the frame that Shadow Basil led me to at the end of the Prologue. I did go to Sweetheart's library, but I don't recall if it had anything relating to BlackSpace. I don't think it even had a key.

Anyway, when this chapter's dream began (friends' room with no friends), attempting to go anywhere else other than the park and the pier (where Mari waits) causes everything to be foggy. This may be the "thick fog" that transpires into the world when "your intentions become hazy", as indicated in the portal left by Humphrey. This may be implying that Omori was not sure about what to do in the dream world, on whether he really should continue searching for Basil (which would lead to the keys, and therefore, to Black Space), and it was Mari that caused him to regain the resolve to do so.

When moving around with Mari, she gets upset if you run too much, saying that her knees can't take it. The portal left by Humphrey also mentions her bad knee. While these are referencing the dream Mari, I am guessing it would apply to the real Mari as well. This may have been the case since before Sunny was even born or at least from a very young age, so Mari having bad knees was a permanent constant and his subconsciousness cannot imagine Mari with healthy knees. This adds some significance to the window as well, because Mari didn't actually get to play outside with her friends very often, due to her knees, and so she mostly watched them through the big window instead, regardless of whether she was playing the piano or not. I considered whether her knees were so bad that she couldn't even walk irl, but one of the book passages (in the portal after beating up Sweetheart) indicated it an hour has passed since Mari "climbed down her ladder". If she can climb down ladders, then her knees shouldn't be that bad, right? Still bad enough that Omori made her always sit in a picnic spot in later cycles, possibly because her handicap got her killed in previous cycles, but that didn't stop her from leaving it to help Omori, as she did this time to help him overcome his fear of drowning, guiding him to the Deep Well.

But in the real world, was Mari actually capable of swimming with her bad knee? How was she able to save Sunny when he fell into the lake? Did she jump in to pull him up, only for herself to drown due to her bad knee...? No, I don't think that was how she died, as it doesn't fit with all the other hints about her death, but it is a possibility. I think she was actually able to swim, and managed to save Sunny without any casualties from that particular incident. In fact, maybe she wasn't even sure if she was able to swim, but she desperately wanted to save Sunny, thus overcoming a challenge of her own, which further helps Sunny see her as a symbol for overcoming obstacles and fears.

So how did she die? Up until Humphrey, I was at least confident that Basil was unintentionally responsible for her death. Now I am not so sure. From the portal left by Humphrey, the flower boy (Basil) will always find the "path to the truth" (Black Space) and Mari will always guide Omori to it. And shortly after that is the statement: "It is their nature. They are the only ones who know... and one has carried it with her to her grave". They are the only ones who know... what, exactly? The truth, of course, as the context is about the path to the truth. But the truth about what? Here, I believe it is referring to the truth about Mari's death. While Aubrey seems to be blaming Basil for Mari's death, it seems she is not actually aware of the truth about what happened. Mari and Basil know the truth, as well as... Sunny, I believe, for this truth is hidden in Black Space, which likely represents the memories and feelings that Sunny is trying to suppress.

In fact, this is probably my wildest theory so far: perhaps the one who is truly responsible for Mari's death... is actually Sunny. But the only ones who actually know this are Basil and Mari, with Mari taking the secret to her grave. Aubrey at least thinks Basil was responsible, which explains why she targets him for her bullying, taking the photo album because she wants to protect the memories of Mari from the person that I'm pretty sure she sees is the one who killed Mari, and Aubrey even subconsciously pushed Basil into the lake (the lake that may somehow still be related to Mari's death somehow). But maybe everything she blames Basil for, consciously or subconsciously, should actually be directed at Sunny instead.

Sunny's reaction to Mari's death is certainly the most severe out of all the friends. While Hero refused to step outside for a year, it was at least 3 years for Sunny. And even now, he wouldn't go to the treehouse or the piano room, except when Hero and Kel step inside the latter first, and, more disturbingly, subconsciously refuses to perceive the closet, see it as part of the wall instead. In his dreams, Sunny has discarded his name and adopted the persona of Omori in order to forget the truth about Mari's death. This truth, sealed in Black Space, is what the "Dreamer" wanted to eliminate from this world. But not only will it linger in his subconsciousness no matter how hard he tries to forget, the Basil within his dreams always finds the Black Space first. I think this represents how no matter how desperately Sunny wishes to completely forget about the reality of what happened, his subconsciousness is aware that the real Basil is aware of the truth, or at least, is aware of enough details to deduce the truth about Sunny being responsible, so Sunny's efforts into suppressing the truth will never be completely successful. This manifests in the Basil of his dreams always being drawn into the truth, into the Black Space.

Meanwhile, the Mari in his dreams represents an opposition to Sunny's efforts to seal the truth. She represents the aspects of his subconsciousness that not only recognizes that concealing the truth completely is impossible (as long as Basil is alive), but also recognizes that attempting to forcefully forget the reality is not a healthy solution whatsoever. So she guides Omori to find Basil, i.e., to Black Space, through the hangman keys, so that Omori can accept the truth, becoming Sunny, instead of rejecting it. She misses Sunny after all. This also means that she wants Sunny to (i.e., this component of Sunny's subconsciousness seeks to) reconcile with Basil, not only in his psychological perspective, but also likely in his physical interactions as well.

This also explains why Sunny sees Basil as the 3-pronged shadow in the mirror reflection in the real world. The shadow represents the truth about the incident that Sunny is trying to suppress, the darkness of his own guilt. The truth that refuses to fade into oblivion because it still lingers within Basil and Sunny, so Sunny sees this dark shadow figure reflected on Basil as well as when he confronts his own fears. It's possible that the darkness manifesting in the bathroom reflection was specifically due to Sunny fearing at that particular time that Basil's distressed state might lead him to discover the truth, or worse, to expose it to others, which is why the shadow appears at that particular scene, whereas other interactions with Basil do not have anything like this.

Meanwhile, from Basil's perspective, it's possible that he doesn't consciously know the complete truth, but probably knows enough that he could figure out the missing details. And even if he does learn the truth, it's not in his character to actually blame Sunny for what happened. Sunny is still his dear friend, and iirc he even described Sunny as being like our "baby" of sorts in the photo album, being the youngest of them all, that needs to be protected and cared for. So even if he does realize that blaming Sunny could protect him from Aubrey's bullying, he would not betray Sunny like that. And I think it's likely that his friendship with Sunny is causing him to subconsciously avoid thinking too hard about what happened, thus preventing him actually considering the possibility that Sunny is responsible for killing Mari.

Okay, but this theory is still missing the most important foundation: how is Sunny responsible for killing Mari? That... I do not actually know. It could be from Sunny freaking out by the spider and falling from the statue, causing Mari to save Sunny and drown in turn, which would explain Sunny blaming himself, but as I mentioned before, this doesn't seem too likely, nor do I think this would cause Sunny to actually break down to such an extent if that were the case. I think Sunny's involvement in Mari's death is a lot more disturbing, but I can't figure out the details. Of course, I am confident that Sunny did not consciously intend for any harm to come to Mari or any of his friends, so I do still think this was an accident of sorts, but still one where Sunny perceives that he is the one responsible for Mari's death. Perhaps, part of the reason why he refused to leave the house for over 3 years, even when his treasured friends knock, is because his futile commitment to seal the truth requires him to deceive his friends. While Sunny may not have realized it yet, it is also causing immense turmoil on Basil as well, due to whatever it is Basil knows about this incident.

The closet probably contains something that would remind Sunny of the actions he took that unintentionally led to Mari's death. It might even somehow be the violin that led to this, but it's hard to connect that to somebody dying. Maybe Sunny snuck out of his violin lesson to play with his friends without telling Mari, and that is what somehow led to her death? Doesn't make much sense, but I really can't think of much else. I want to see what is in the closet.

Okay, I think that's enough about this wild theory about Sunny being the one responsible for Mari's death. I am not very confident in it, and I am not giving up on my earlier theory (from before I started the dream segment of TWO DAYS LEFT) of that Basil is the one responsible for Mari's death, but the latter seems a lot harder to reconcile with the details revealed from the portal left by Humphrey.

The portal left by Humphrey also talked about the your friends meeting an "unfortunate fate" many times. While I don't think relates to discovering the truth about the past, it may be a warning for the future. They are "revived time and again", but the "most haunting stay in this world, even if only their bones remain". This makes me wonder if the previous iterations of Kel/Aubrey/Hero from earlier cycles may actually still linger in some form. I don't think I encountered anything that could relate to the "bones" that remained, so maybe this will haunt me in the future.

Speaking of Humphrey... what does Humphrey actually represent? Now, the Branch Coral in the Deep Well mentioned three great creatures: the oldest, the wisest, and the favorite. The "oldest" one almost certainly refers to Humphrey, since it was mentioned that he lives here, just beyond this cavern, and it also fits the other description that "age has removed his conscience and he has evolved into a parasite within himself", where you see a bunch of "Humphrey" pop up inside the Humphrey whale as Diglett-like moles. The "wisest" committed an act that opposed the Dreamer's will, was stripped of her wisdom, and banished to isolation in a special prison deep deep down. I haven't gone anywhere deeper than the Deeper Well, but I am speculating that the "wisest" is the creature for which these tentacles are emerging from, since they show up even in the Deep Well. The "favorite" is the big yellow cat, who watches over the friends' room, that we see near the start of every dream chapter. Since all three of these are in the dream world (or headspace), they must have arisen from Sunny's subconsciousness. I do recall a big yellow cat in the real world, specifically a statue in the park (which is not as big as Sunny remembered it being, likely due to Sunny's aging), so I suspect that is where the big yellow cat came from. Sunny probably associates it with the fun times that he has in the park, playing with his friends, which is why it watches over the friends' room. However, I have no idea where Humphrey the whale comes in, or the "wisest" creature with tentacles, but I should try to look out for any hints about them when I get back to the real world.

The Branch Coral also said that Basil (dream) is not in this world, which makes sense, as he is likely in Black Space. More notably, the Branch Coral also stated that "he is special to you" and "a string of fate ties you two together". "To retrieve him, you will have to remove yourself as well, but in a way that is natural for this world". This gives me the impression that Sunny's salvation is tied to Basil's, which fits better with my theory about Sunny being the actual one responsible for Mari's death, because it is only by confronting the ugly truth that Basil can be saved from the misunderstanding that he was the one responsible, and while Sunny would still suffer immensely from recalling this reality, it allows for a better possibility that he would be able to move on from it, allowing his friends to forgive him, as opposed to trying to suppress the truth to the extent that he ends up cutting off all contact with his friends.

"A hanging black light bulb... the repression of an idea." I am not quite sure what this idea is, but my interpretation is that the light bulb being black means that while the idea exists in Sunny's subconsciousness, it is one that Sunny is trying to repress, resulting in the pitch-black interior. Perhaps the idea relates to accepting the truth about what happened in the past, but the repression represents his desperate will to try forgetting about it all instead.

While this chapter had a lot of interesting developments, most of them were at least somewhat related to the ideas I already had, even if some of them caused massive revamps. But there is one that seems to be very different from everything else I encountered so far this entire game. Inside the hole left by the W key is what I assume is a part of black space where a shadow is hacking at a tree with an axe, saying "Stay away... You are not my son..." and then "Why... Why won't you fall?" The tree seems to have a rope hanging, and I am wondering if it might actually have a tire swing (but I can't see the tire because it blends with the black background). The tire swing is relevant, since a tree with a tire swing in Vast Forest is one of the relatively few locations where the 3-pronged shadow figure appeared. Here though, the shape of the rope looks a bit more like a noose, which is even more disturbing. As for the shadow figure... I think the most likely candidate is Mari's father, who I am pretty sure has never been mentioned so far, which itself is quite conspicuous. I don't know if he is dead or if he left, but I wasn't sure how he would be relevant. The statement that "You are not my son" is quite troubling. Could it be that Sunny and Mari have different fathers? Sunny is the younger, so it's hard to imagine that the first father would encounter Sunny, and it makes very little sense that this family situation does not seem to be implied at all from anything we saw so far. But what seems more plausible is that they both have the same father, but "you are not my son" is a strong rejection of his own child, which must have arisen from something really serious. Also, while he is hacking at a tree, I... highly doubt this is reflecting an actual tree in the real world. But it seems more likely that he is hacking at a person in reality, but this disturbing memory tones it down by representing a tree instead. Basil is another possibility on who the tree represents, particularly due to his association with plants, but... I can't see why Sunny's father, or even Basil's father (who actually has been mentioned, kinda, since I am pretty sure Polly said that Basil's parents, in plural, are traveling around), would be hacking at the poor victim. Swinging an axe at someone is pretty serious that I can't understand why nothing in the real world reflects this disturbing incident. We do have a corpse, but it's of a female (Mari), so it doesn't quite fit the "You are not my son" line. Maybe he was trying to swing at Sunny when Mari tried to protect him and took the blow instead? If he hit her in the knee, is that why she has bad knees? If this is when Mari died, well, this doesn't seem to fit with any of the various hints we get about Mari's death. The "Why won't you fall?" and the continuous swinging animation suggests that he kept swinging multiple times, which is unlikely to have happened if someone else took the hit from the first time. Anyway, I am rambling far too much about this scene, and while I am sure it is really important, I am having a very hard time trying to connect it to... basically anything else that drew my attention all game.

---

BEFORE SLEEPING AT BASIL'S HOUSE

Okay, it seems most of my theories were very far off. I couldn't decide whether it was Sunny or Basil who was responsible for Mari's death, but now we find out she killed herself. Seems the only detail I got correctly was that she didn't die from drowning, i.e., she saved Sunny safely after he fell.

Her place of death is now a tree stump, implying that she hung herself. There are some trees in headspace that may be related. A notable one is the tree with a tire swing in Vast Forest, where the 3-pronged shadow figure (Shadow Mari) shows up in. Perhaps there was a tire swing in the tree in front of the tree house, and the same rope holding the tire was used for the hanging (tire removed, of course). That being said, a tire swing wouldn't be hung so high for a person to hang, so the noose may have been re-tied to a higher height, or the entire rope was moved to a higher branch.

Another notable tree is the one in the disturbing area below the W key, where a man kept swinging an axe at the tree, in which an empty noose hung from. If Mari was hung from a really high branch, it makes sense for others to try chopping down the tree to get her down. Or maybe it was chopped off afterwards, possibly to avoid reminding the witnesses (particularly the kids) of the disturbing imagery of the hanging Mari. The "why won't you fall?" might be about the tree being sturdy, but "you are not my son" is hard to make sense of. Did Mari's father reject Sunny after seeing the hanging Mari? Was Sunny actually somehow responsible for Mari's death after all?

After all, there seems to be some dark truth in Sunny's mind, buried in Black Space, which only Basil and Mari know of, with Mari "taking it with her to the grave". But... I am not sure what this truth could be.

Speaking of Black Space, the 3-pronged shadow figure is pretty much confirmed to be Mari, with the "I love you" as she followed you around in one of the Black Space rooms. While there were some hints to this already, particularly the appearances in Sunny's bathroom mirror after pretty much every hallucination of Mari, it doesn't explain why it takes this form or why it shows up in place of Basil at his bathroom mirror. My guess is that this shape is something Sunny specifically saw that he associated with her death. I previously considered it as the silhouette of her drowning figure, but now I know she didn't die from drowning. I'm not sure how that shape arises from a hanging figure; maybe Sunny was only able to see the shadow cast by the sum over her corpse, and it somehow had that shape? As for why he saw Shadow Mari (yeah, I think I'll call her that instead of 3-pronged shadow figure) in Basil's bathroom, my interpretation hasn't changed: Sunny is reminded of Mari's death when he sees Basil, but now I'm not sure if it's because he sees Basil as responsible for her death or because Basil is aware of certain details associated with Mari's death or may even have been directly involved in it. In the dream world (headspace), Shadow Mari likely represents Mari in the state where she died, including any ugly details that Sunny learned about much closer to her death, while the regular picnic Mari represents the caring nee-chan from his older memories, who even saved him from drowning. Omori (not Sunny) adamantly tries to deny the dying Mari, purging Shadow Mari whenever it shows up, except in BlackSpace, which is where the repressed thoughts and feelings are stuck in.

Back to Mari's death, did she really kill herself? I considered whether it could be a murder, but DR taught me that it's pretty much impossible to conceal a murder through hanging. It's possible that the police are aware it's a murder or accident but it is publicly presented as a suicide because minors played a disturbing role, but even then, it would make more sense to cover it as a tragic accident with nobody involved, as opposed to a suicide that would be very traumatic for her friends. Besides, the story themes seems to focused on an emotional mystery as opposed to a murder mystery, so I am pretty sure it's a suicide...

But why would she do it? It's possible that her cheerful demeanor was an act, and she was actually struggling inside, but it still doesn't make sense. Given what we have seen of her character, she would certainly have realized that this action would emotionally devastate her friends, so even if she saw death as an escape for something severely tormenting her, I can't imagine that she would actually go through with such a decision. My guess is that she would only do this if she was in such a disturbing situation that the only alternatives would involve the death of another (Sunny?). This would imply that somebody was threatening her though, with a hostage of sorts. For example, maybe somebody was molesting her, threatening to kill Sunny if she didn't comply. I don't think this game would really go that far, but I can't see how this could arise from a milder situation. I guess it might make sense if she did something horrifying, e.g., she killed someone, and the guilt and/or shame overwhelmed her to suicide. It's not a very rational decision, but people under such immense emotional stress generally don't act rationally, and it was really important for her to preserve the wonderful caring nee-chan model to Sunny and the other friends (so disclosing her action wasn't a consideration).

So how does Basil tie into all this? Unlike Kel, Hero and Aubrey, I think Basil is aware of the reason why Mari killed herself, or at least, he is aware of some of the disturbing details to be able to form a good guess. It likely involves Sunny as well, who also knows the truth, but is desperately trying to forget it all.

If Mari killed herself, did she leave behind a suicide note? If so, who read it? Hero, Kel, and Aubrey seem genuinely confused by why Mari killed herself. Mari would figure how traumatizing her death would be to her friends, so she would have left a note to help them deal with it better, even if she had to lie in it to comfort them. But with Hero, Kel, and Aubrey in the dark, I suspect that they did not read the note that she left. Did someone hide it away? Did Sunny place it in his closet? Did Mari leave the key to the toybox in the treehouse, so that the others can find her suicide note? Did she anticipate that they might not be ready to revisit the treehouse, so she wanted them to take their time to recover until they return and find the key? I don't know exactly what she intended, but I do think the toybox is where Mari placed her suicide note, or probably her diary, so that the others can eventually learn what she was going through. Note that the photo itself was taken by Basil, and he would keep it in his photo album, further implying he is somehow involved.

There are four things that stand out to me, and I suspect at least one is related to Mari's death, but I still can't conjure up a solid coherent theory for any of them:

1) Mari's Dad, and to a much lesser extent, Aubrey's Dad. Neither were mentioned at all until One Day Left, and only in passing. Mari's Dad is the more conspicuous one since she's the one who died and her brother is the one whose perspective we are following. The player's observation is subject to Sunny's perception, as evidenced by the vanishing closet, so maybe he also subconsciously blotted out anything related to his father too.

But what particularly makes their father suspicious is the figure chopping on a tree with an axe, under the W key, with "you are not my son" being a particularly strong line. Did he reject Sunny after seeing Mari's corpse? Or was it before, and did it somehow lead to Mari's death? Was he really hacking at a tree with his axe, or was it something else in reality, like a person? If Mari really was being threatened (with someone else like Sunny as the hostage) or if Mari herself killed someone, by top suspect is her Dad.

Aubrey's Dad is also unmentioned until One Day Left, but he lacks that direct connection with Mari, so he's probably not as significant. Still, Aubrey's Mom is a complete mess right now, and it seems Sunny and Aubrey got hit the hardest from Mari's death, so maybe their suffering was exacerbated by their fathers leaving the picture (in some form), and this might not necessarily be a coincidence.

2) The recital. What exactly is this recital for? I initially assumed it was just for a school event, but too many smaller clues link to the recital. Mari learned the piano to play at recitals. Sunny started learning the violin to play with her. He felt pressured to continue learning even when he no longer wanted to, as he preferred to chill with his friends. The violin was wrapped like a birthday gift, but it wasn't from his friends (who pooled together to get him a "building block set"). The violin is nowhere to be found; it might be in the closet. The piano has OMORI etched into it. The large curtain behind the piano shows up in headspace in the only time where Mari seems to revert to her true colors, while she references her death, apologizing to Sunny (yes, Sunny, not Omori). Mari's corpse was found on the night where she was supposed to have a recital, the first one which Sunny was supposed to join.

There is no way all of these are simply unrelated coincidences, and yet, I can't find a clear coherent explanation to resolve this. I would guess that Mari's Dad might be the one who got the violin for Sunny, pressuring him to learn so he can play alongside Mari. The recital probably has some special significance to their dad, like maybe he earns a lot of money through Mari's piano skills. These are wild guesses though, and barely explain any of the relevant mysteries.

3) Mewo. Where is Mewo? We saw Mewo only once in the real world, when the four friends are going from Basil's house to Sunny's house, intending to finally revisit the treehouse. Mewo hops away towards Sunny house, but we don't find him in the neighborhood or anywhere. Sunny is known to hallucinate, so that Mewo might not have been real. Did his resolve to go to the treehouse, to visit Mari's place of death on the way, remind him of Mewo?

What makes Mewo particularly significant is that he has always been in WhiteSpace. This suggests an incredibly strong bond with Omori. Mewo was a companion that Sunny could play with anytime at home, even late at night when his friends are in their homes to sleep. His absence in the real world is very concerning.

There is also one BlackSpace room, where a big black cat in a suit says that Mewo has been very bad. Mewo is on the counter, and for some reason, examining him gives Omori the prompt to cut him up. I didn't do it, so I don't know what happens (preferred to stab myself), but this is very disturbing.

4) Fingers and dismembered bodies in general. One of the BlackSpace rooms shows various dismembered body parts. Like Oyashiro-sama's first year victim. As disturbing as this is, this particular room was not emphasized as being particularly significant. However, the last room I've been in was certainly highlighted. It's at the very end, after the church where Basil is consumed and then through the treehouse door where Basil is taken. The room was all red, like blood, and there were... fingers... lying around, cut off. Just fingers.

Back then, I thought this was about Mari's death, before I learned that she killed herself. A hanging should not spill blood, nor should her fingers be cut off. If even one finger was cut off, the police should have investigated this as a murder instead of concluding it was a suicide.

So then... what were the dismembered fingers?

All four factors are really bothering me, and I'm having a really hard time in making sense of them. Here is my latest wild theory:

Mari is a talented pianist, to the delight of her friends and family. But her father sought to capitalize on her talent, having her play in various big events where he would be paid very well. Mari wasn't paid, but she didn't mind, as she loved playing the piano and might not have realized that her Dad was profiting from it anyway.

Sunny loves his nee-chan and wanted to join her. His father saw this as a business opportunity, deciding to buy him a violin and hiring a private tutor to teach him how to play, intending that both kids would eventually be able to play together in recitals that he would charge more for, earning more money.

Let's tie Mewo into this through the carpet stain incident. At some point, while the friends were playing in Sunny's house, Kel accidentally stained the carpet. I think he spilled Orange Joe iirc. Mari was very upset by this, and scolded Kel harshly. This event was mentioned when Kel and Hero enter Sunny's house in Two Days Left, and the stain remains to this day.

But maybe the reason Mari was particularly upset was because she was scared of her father. When he saw the stain later, he demanded Mari to tell him what happened. Mari realized that Kel would be in a lot of trouble, so she lied and said it was Mewo peeing. To her horror, he then proceeded to strap Mewo in the kitchen counter and prepared a knife. He made both Mari and Sunny watch him slice up poor Mewo, despite their protests. He told them that Mewo was being a very bad kitty, knowing that this event would terrify Mari and Sunny, ensuring that they submit to his authority. He might have even forced Sunny to cut up parts of Mewo as well.

With such a father, it's no surprise that Sunny grew up so quiet with an emotionless expression, repressing his feelings, afraid of how his father might react if Sunny spoke out. There may have been more incidents of animal cruelty, maybe involving a fish (Humphrey) or an octopus (the wisest), to the extent that Sunny grew desensitized to the suffering of animals. He probably saw his father slice a horse into two, with the two pieces roaming Sweetheart's courtyard in his dreams. Sunny himself may have killed bunnies in the real world, to his father's encouragement, and thus carried over to his dreams. Mari was heavily troubled by all this as well, but she forced herself to put up a cheerful front for Sunny's sake, a strong pillar of support for her otouto. She couldn't stop him from killing animals, but she at least convinced him to keep it a secret from their friends.

Maybe at some point, Mari may have found out her father had killed someone. He asked for her help in dismembering the corpse, threatening to kill Sunny if Mari refused or spoke a word of this to anyone. Mari was coerced into submission, desperate to protect Sunny. There may have been more events of this nature, emotionally shredding Mari inside, but she put up with it all for Sunny, and forced herself to smile for her brother and her friends that she truly loved and cared for.

Having to cut up human corpses for her father, Mari could no longer bring herself to raise a knife in the kitchen, not even to cut fruits and vegetables, and could not stand the sight of raw meat. There was no hope in her being able to cook. Hero may not have known the reason for this, but he strived to compensate for her weakness, and learned to be an excellent cook himself, so that he could do all the cooking for Mari's sake. Mari truly appreciated this, and treasured all her friends. Her love for them kept her alive, retaining her sanity.

She continued to perform at recitals for her father, not being paid a cent, knowing it would be foolish to resist. But she loved playing the piano for Sunny, who found comfort in her music. Sunny, however, was not enjoying his violin lessons. It was much harder than he thought it would be, he lacked the talent, and it cut down on the time he could play with his friends. But he wouldn't dare to tell his father to end them, until it was close to the date of what was supposed to be the first recital where he would perform with Mari.

He only confided in Basil regarding his desire to quit the violin. He did not even tell Mari, because it seemed she was really looking forward to playing with him, and he was unaware of her own suffering. Basil encouraged Sunny to confront his father, and they decided to break the news probably the day before the recital.

On that fateful day, Basil came over to support Sunny. Mom probably wasn't home, maybe going out shopping. Sunny faced his father, probably in the area in front of the treehouse in the presence of Mari and Basil, telling him he wanted to quit playing the violin. Mari understood and supported his decision, but was also afraid of how her father would react. He was furious. The recital was already scheduled, and he was gonna earn a lot from it. Quitting now would have been a huge loss, and may hurt his reputation too. This was unacceptable. Emboldened by Mari's and Basil's comforting presence, Sunny stood his ground, opposing his father. The father grabbed an axe, declaring that Sunny was not his son, and violently started swinging it, seeking to kill Sunny. Or maybe his target was Basil for poisoning Sunny's mind, making Sunny defy his father instead of continuing as the obedient slave to his father's ambitions.

While Sunny feared that his father would get violent, he probably didn't anticipate it getting this bad, with his father's utter rejection of his son and the determination to kill Basil. Mari had no doubt that the father would certainly kill Basil, and in her emotionally distressed state, she grabbed the steak knife and killed her father, catching him by surprise, to protect Basil. She may have unleashed all her accumulated hatred for her father over the years, stabbing him until he was no longer moving, with Sunny and Basil watching in shock. She may have cut up a few of his fingers, which flew in front of Sunny.

The father was dead. Once Mari came to her senses somewhat, she realized what she had done and that they needed to dispose of the corpse. From past experience with her father's victims, she knew that the soil here was inconsistent, and there was no place to dig a hole big enough for the corpse, and so they would have to dig multiple smaller holes, just as she helped her father with before. She ordered Basil, the resident gardener, to start digging, but she needed Sunny's help to dismember the corpse. Sunny cut up animals before, but never a human, and this was his father. Knowing that her brother had an active imagination and wanting to preserve what remained of his mental state, Mari tried to talk to Sunny, manipulating him into imagining that this was not a human corpse (certainly not his father!), but it was actually the corpse of a black cat, just like the first corpse that Sunny had ever cut. She knew how to get through her brother and it worked, with the two of them cutting up the corpse (which Sunny imagined was a big black cat) and burying it in the holes that Basil dug. Once they were done, the three of them were probably too exhausted, mentally and physically, to reflect on what happened, so I am guessing they didn't talk much. Mari escorted Basil home, lulled Sunny to sleep, and probably told her Mom (when she came home) that her Dad had to go to work and they wouldn't see him until the recital, stalling for time. It's possible that her dad was supposed to be heading out anyway, and Sunny confronted him before he left, so his absence was not unusual.

The next day, Kel, Hero, and Aubrey were out shopping, preparing for the big recital. The reality of the previous night started to dawn on Mari, Sunny, and Basil. Basil stayed holed up in his house for the entire day, afraid to face anyone. Mari was starting to acknowledging the reality that she had just killed a human being, and it was her father no less, despite how vile of a person he may have been. Even worse, she forced her own brother to cut up the corpse of her father. She tried to talk to Sunny, but Sunny did not react well. Not being fully aware of his father's crimes, the memory of Mari stabbing their own father to death was too much for Sunny. He might have even said some harsh words against Mari, before locking himself up in his room. Overcome with the guilt and shame of killing her father in such a deranged manner, in front of her own brother and then forcing him to dismember the corpse, Mari could not handle it anymore and resolved to take her own life. She hid her diary, where she spilled her true feelings over all these years and documented the crimes of her father, inside Sunny's toy box, which was in the closet. She locked it, with the key taped to the back of one of Basil's photos, placing them both in the treehouse, hoping that maybe one day, her brother may eventually understand what she went through. She may have left another suicide note for her mom to find, and then proceeded to hang herself in front of the treehouse.

Her friends were distraught, and couldn't fathom why she would do what she did. Sunny and Basil, however, had an idea of what drove her to this state. The shadow of Mari's corpse over the grass was permanently etched into Sunny's mind as the 3-pronged figure, and maybe the center of the shadow lay over the spot where their father's head was buried, so Sunny imagined the eye of his father, oriented vertically, staring out from the center of this 3-pronged shadow figure. Sunny regretted his harsh words against his sister, recalling how much she loved and cared for him, and he blamed himself for effectively killing Mari. He may have even contemplated taking his own life like Mari did so he could join her, but he knew that she would have wanted him to live on.

The police and some adults (like their Mom, in particular) may have realized that the Dad's disappearance is suspicious. They might have suspected that Mari might have killed him even. However, they couldn't possibly disclose such information to the children, who were already having a hard time. The official story to the public was that the Dad was so disturbed by Mari's suicide that he left the rest of his family and skipped town. Only a few individuals (like their Mom) was aware that this was not what happened.

Sunny and Basil never spoke again about that night. Sunny eventually stopped going to school, and eventually stopped leaving his house altogether, trying to overcome his sorrows by indulging in happy adventures in the dream world. All the dark secrets about Mari were banished to Black Space, and his regular dreams featured the happy and cheerful Mari-nee that he remembered from before that night, guiding and protecting him. Despite his desperation to forget what happened, it would always eventually resurface in his subconsciousness, manifesting as falling into Black Space in his dreams. He went so far as to imagine himself as a new person, a blank slate with a new name. He named himself Omori, which was one of his childhood personas that he even etched onto Mari's piano. He intended for Omori to be a resident of headspace, having lived in whitespace for as long as he can remember, with none of the memories or darkness that Sunny carried. These desperate attempts to forget all the unpleasant details of the reality helped Sunny cope with what happened, but the truth always remained buried in his subconsciousness, no matter how much he tried to erase it. Also, he now sees his father as this big black cat in a suit, but he only shows up in the sketchbook and in BlackSpace.

Meanwhile, Basil struggled immensely as well. He sought solace in the only other person who knew the truth of that night, but Sunny chose to lock himself up in his house, which made it even harder for Basil to cope. His parents realized that Basil was extremely disturbed by Mari's death, and suggested that they take Basil with them to their travels in various other places, away from the town that holds such a traumatic memory. Basil refused, insisting on remaining with his friends. But he was no longer seeing his friends, as they were also coping with Mari's death in their own ways. Basil instead focused on the photo album, trying to recall the moments he had with them. His parents felt that Basil's attachment to his friends was very unhealthy, and that he needed to move on from Mari's death, so they decided to... scribble on all the faces in the photo album, including Mari, hoping that it would help Basil recover. It backfired when Aubrey found the photo album with the scribbles and then she lashed out against Basil for doing something so horrible. Even so, Basil insisted that he should stay, and his grandmother convinced his parents to let Basil stay with her, and she would look after him. With her ailing health though, it was eventually Basil who had to look after his grandmother. His responsibility towards his grandmother and to his garden is what motivated him to keep living on, while desperately hoping he could return to the happy days with his old friends. When Kel revealed that Sunny was moving out, Basil was driven into despair, because he would then be the only soul in the town who knows the truth behind Mari's death, and he still has not been able to even talk to Sunny about that night. Even when Sunny came to the bathroom, he looked into the mirror and was reminded of Shadow Mari, and he then proceeded to leave before Basil could actually try talking to him properly. Once his grandmother passes away on One Day Left (okay, this isn't explicitly confirmed, but it's extremely likely to be the case), Basil probably intends to kill himself once Sunny leaves town, unless Sunny can finally take the step towards reconciliation.

So there you have it. There are a gazillion holes in my fanfic, with a lot of unsubstantiated speculation, but hey, at least I tried. I do think Mari's death is so inexplicable that the actual circumstances must have been really crazy to lead to this.

That being said, I am somewhat confident that there is some dark truth that only Sunny, Basil, and Mari know, which may relate to Mari killing herself. And I think the proper way forward would be for Sunny to reconcile with Basil, possibly disclose the secret that they share to the other friends. Opening the toybox may allow all of them to better understand what really went on in Mari's heart and in her mind, leading to her death. And the five remaining friends can promise to stick together and move on to a brighter future.