acquisitive invader part 2 !

Stage 4: Darkness Surrounded by Rocky Crags
(Location: Cave entrance)
BGM: Torch-Bearing Cave Exploration

Boss: Gold-Colored Bat, Sayori Hibiki
-A youkai bat who lives in the cave that the triangles are all pointing to. Pretty chill.
 Since she's skilled at echolocation, the culprit asked her to guide any visitors through the cave.
 Which she does, once the protag beats her in a fight.

BGM: In the Dark, With a Perfect Field of Hearing

Echo Sign "Echolocation"
Reverse Sign "Upside Down"
Bats "Golden Bat Cluster"

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Stage 5: Dwelling of the Water God
(Location: Cave depths - Limestone cave)
BGM: Mystic Flow

Boss: Platinum-Colored Dragon, Ryuuko Iwaizumi
-A dragon (an actual 龍, for that matter!) with powers over fluid motion.
 She got sealed in the cave for doing Evil Mischief (TM) back in the day,
 but now she's mellowed out enough that her fellow cave youkai all turn to her as a source of wisdom.
 She offered advice and information about Gensokyo to the culprit upon their arrival, and sends the protag off to see her.

BGM: Silver Dragon of the Underground Lake

Fierce Flow "Endless Eddies"
Flowing Motion "Dilatant Fluid"
Star Sign "Limestone Cave of Shooting Stars"
"Dragon God's Reversed Scale"

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Stage 6: A Desire for Knowledge Crossing Time
(Location: Limestone cave, deepest region)
BGM: Deep-Layer Limestone

Midboss: Ryuuko
-Just tagging along to see what happens.

"The Flow of Time is Incessant"
 (*ref to the passage "the flow of time is incessant, and yet its water is never the same" from the Hōjōki)

Boss: Artificial Intelligence from a Future World, MANA-001
-A learning android who arrived from the distant future, driven by the desire to acquire knowledge about the world around her.
 Despite being celebrated as a cutting-edge learning AI, she was eventually slated to be scrapped by her creators out of fear
 that she might become uncontrollable, so she hopped in a time machine and fled to the perfect place of refuge: Gensokyo.
 She stays in the limestone cave to keep her processors cool most of the time.
 After learning about Spell Cards and incidents during one of her book-collecting trips to the village,
 she decided to try her hand at starting an incident of her own.

BGM: A Certain Android's Timespace Voyage ~ Diverged Epistemophilia

Initialization "Randomly-Launched Danmaku"
Differential "Symbol of Nabla"			*https://en.wikipedia.org/wiki/Del
Deep Layer "Deep Neurons"
"Hospitable Generative Network ~ Witch"
"Singular Future"

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Ending: Mana comes to visit Marisa's house, now equipped with a sun parasol, and offers her a Future Tech (TM) of her choice. Marisa picks one of the all-purpose handyman robots that Mana had tasked with drawing triangles all over the place, since it ought to be helpful for cleaning her house. ...But Mana neglected to completely wipe the triangle-drawing program, so Marisa wakes up to find it scribbling all over the living room. She vists Mana again to trade it in for a fixed version, but can't bring herself to trust the new one either. Tragic.

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The end! Mainly inspired by the creator (Nokizaki Fuurin)'s recent studying of AI-related topics, plus source material from their home prefecture of Iwate (particularly its "Dragon Spring Cave" limestone cavern).