If you want a micro summary, it's kinda like this at the end: imagine we're at about chapter 210 but "Kumoko" hasn't become god yet - she's still Arachne. Shun story ending is pretty similar to WN - Shiro turns up after Shun hits Taboo 10 and is recognised as "Wakaba Hiiro". On "Kumoko" side her previous life's name has been officially revealed (by "Maou Shojo Ariel") though she isn't called Shiro/Shiraori yet. "Kumoko" and Ariel have officially teamed up - Mera and Sophia are with them.

"Heroine" Ronant doesn't appear in the story at all but he does appear in the author's afterward. (lol). There wasn't enough space to to include him it seems but he should appear in the next volume.

I have mixed feelings about it. On the one hand, we'll get something I thought I could only dream about - "Kumoko" raising Sophia while still being Arachne (though I was hoping for them to be by themselves). On the other hand, there's no Ronant and a bunch of interesting things was skipped over. The Shun side stories weren't as interesting as in the WN - it's even more tropey shonen-like than before and is basically Shun and co trying (and totally failing) to even injure Sophia. The pacing is better overall and flows more naturally but some things are done a bit too fast, I thought. Kumoko hasn't learnt about the delights of alcohol yet either btw.

Long summary of the "Kumoko" chapters:

As before, Kumoko analyses Sophia's skills, titles etc and comments on them. And simply leaves. She's much more jealous than in the WN though. Afterwards, she tracks the carriage Sophia is in from a distance and sees the town it gets to. She comes across (and kills) some elves while at it. She's surprised to come across "elves" (fantasy!!) and even more surprised that her Parallel Wills don't react the same and clearly don’t like elves - she feels that they've been getting odd since they returned from attacking Mother's soul (they basically absorbed some of Ariel’s feelings). Kumoko is increasingly creeped out by the differences between her and her Parallel Wills throughout the book because they feel like strangers to her.

There's some amusing scenes from Dustin’s POV and Potimas's POV (in that time) as they're both wondering what the heck is going on and they both think that Ariel is interfering for some reason (since a spider is involved). The elves were going to kidnap Sophia but Kumoko had randomly found and killed them. Incidentally, Potimas considers Oka-chan and the reincarnators to be like a gift from god (though doesn’t consider the “administrators” to be god) and is particularly happy with Oka for telling him so soon, and otherwise treats everyone like trash.

Kumoko healing the people and getting sweets etc is more or less the same. Kumoko starts learning the language manually. Same as before, nasty guy from Otsu country turns up and causes problems. We actually see some scenes from the POV of Sophia's father - he’s struggling to understand the situation, particularly as things get worse.

In the WN, Kumoko absorbed Mother around this point and then Ariel attacked but we get neither. Instead the war happens as before and Kumoko interferes as before (her first attack kills several thousand people) but that's when Ariel turns up to kill Kumoko with Abyssal Magic. In the LN, Ariel doesn't have a cheat skill to prevent others from running away but she does use similar barrier magic that the ancient Earth Dragons used on her to block any high powered spells (ie teleportation). Ironically, the Hero (Julius) being on the battlefield almost helped save Kumoko - Ariel has to be cautious of the Hero Title (as explained in recent WN chapters).

Kumoko dies and revives as before and the "babies" are born. However, instead of Kumoko being a sponger and taking a long time to revive, ironically it's Gyurie who comes to help her - he brings her a load of high quality food. Previously he had met up with Ariel and had teleported Ariel to where Kumoko was on the battlefield, feeling this was the most he could do to oppose Kumoko without D erasing him. He actually brings the corpses from the ancient dragons that Ariel had killed (though that scene of her fight was mostly cut out). Gyurie apologies for his previous actions and says the dragons died to help Kumoko. They also have a conversation a bit like in the WN when Kumoko had just left the Labyrinth for the first time - she tells Gyurie that he should do what he wants to.

Because of the food, Kumoko is able to revive quickly and is also able to evolve. We see her level 1 Arachne stats - average is around 40,000 with magic being about 44,000. However, she notices (using clairvoyance) that Sophia's town has been attacked and goes to save Sophia by herself. Situation is quite similar to WN except Kumoko is still Arachne and Potimas has a top spec modern "Gloria" robot (a more modern and much nastier version of the one Sophia fought). Kumoko saves Sophia and heals Mera as before and thinks about eating Sophia - then loses her appetite when Sophia pisses herself. Hands Sophia back to Mera.

However, this is when Potimas uses the anti-magic magecraft of the Gloria and Kumoko is in a similar situation to facing that robot army in the WN in that she can barely use any skills or spells. She's able to make some progress, forcing Potimas to reveal various combat features he had wanted to keep hidden, but is basically in deep trouble against just one modern robot. Ariel turns up to save her (with some lines very much like how she saved Sophia in the WN) and is in full "zannen" mode :D

Kumoko wants to run away but doesn't get a chance. She's worried because she has no spare revival eggs currently. However, Ariel doesn't know that and offers to team up with Kumoko - after the soul merge and with Kumoko being functionally immortal Ariel doesn't feel like fighting any more, and calls Kumoko scary. After a lot of pondering, Kumoko eventually agrees (btw, she barely speaks at all - I think maybe one spoken line from her in the whole book) and shakes hands with Ariel. Ariel loops in Sophia and Mera like in the WN and they all agree to go to the demon territory, though the initial plan is to go to the capital of the country of Sariel first.

Flash forwards ~15 years and Ariel is beating up one of the spider-ish-type robots in the elf village, thinking back on those events, and tells Potimas (through the robot) that she's come to finish off him for good.

At the end, Kumoko has put all her Parallel Wills into her “babies” (9 babies get one copy each), largely letting them do whatever they like though Kumoko also has a plan to kill all the humans and demons with them.

--- On the Shun side of things:

Early on there is a small chapter from the POV of Feyrune (the dragon reincarnator), and she regrets that she bullied Wakaba Hiiro in her previous life. She had wanted to apologise to Wakaba when they meet again but then she heard that Wakaba had died and so feels she'll never be able to clear her regret. She feels that her being a dragon is "punishment" - normally meant in a "bad karma" type way but can also mean "punishment from god". D, it's you!

There is some talk from the other reincarnators about how Wakaba Hiiro was really quiet in class and slow to answer. "Kumoko" does have some thoughts on this herself about how she used to be in her previous life - she says that she would "freeze" when people talk to her or she needs to talk or similar. Which is why she's happy being a loner.

At the end of the Shun timeline, Sophia is "playing" with Shun and co and is basically protecting Yuugo. Kyouya/Wrath turns up and says that time's up (playtime is over) as the Demon King army is here now. Oka-chan knows that Wrath is the 5th Army Commander and demands to know what he’s thinking. Around this time Yuugo gets angry and calls Sophia "Rihoko" (first time it's revealed that Sophia = Rihoko in the LN) which makes her really pissed off. Sophia’s rage scares everyone a lot (like what Wrath did to Kanata in the WN), except Wrath.

Shun is currently having "Taboo" installing (which causes pain but doesn't seem to knock him unconscious) when he notices someone put a white hand to Yuugo's head and a spider comes out from his head and that spider is absorbed by the new person. Yuugo collapses to the ground like a puppet whose strings were cut, revealing an all white girl (Shiro). Sophia says "Please don't interfere, goshujin-sama". From her appearance (all white) and Hyrinth's reaction, Shun guesses that this person is the one who killed his brother (in the LN, Shun doesn't see the event in the memory crystal). Oka-chan is really shocked of course. Shiro nods her head at Oka-chan and says "It's been a long time, sensei".