You know, I forgot to add the horror tag until last chapter.
What's most horrific to me is Michi's breakdown. Nothing says terror induced insanity like screaming at the monster "I don't know you're there." It's the total desperate abandonment of her policy, and that might just be what's needed at this point. Because it's hard to believe but the festival arc hasn't hit its climax yet, and Michi's not about to get time to rest and think this one over.
Aizawa
It's finally confirmed Michi and Aizawa knew each other pre-memory loss, but what's also surprising is Aizawa seems to have never forgotten anything. She's hanging on by a thread to Michi remembering her, and so it also seems confirmed her desire is to never be forgotten. The play at the start is incredibly unsubtle about its parallels to Michi and Aizawa, going as far as to implicate Michi's life is in danger if Aizawa isn't satisfied.
But in my eyes there's a bit of a misdirection here. Aizawa wasn't threatening Michi at the end, she was painfully passing on. Her grotesque transformation was triggered by Michi denying she'd ever known Aizawa, not with her being seen. We already saw what happens when Michi acknowledges her back in chapter 12: reality bugs out and Michi gets her memory wiped. And I think that might be a defense mechanism warding against this exact scenario. If Michi can't talk to Aizawa, Aizawa can't find out she doesn't remember her. Which still begs the greater mystery of why Michi lost her memories in the first place.
It also seems likely Aizawa knows Michi can see her, if the screaming didn't give it away.
Back in chapter 13, Karasuma commented on both how the school has a barrier in place keeping dangerous ghosts out (but letting weak ghosts in) and how young Michi's powers were fading. That barrier seems to be gone, as well as the mark that allowed Aizawa to follow Michi around school? Aizawa would already be in enough trouble with that if right now a ghost weren't hijacking Ange to get in.
And yes the implication's that Ange is possessed. She suddenly calls Theia "chan" when she normally uses "san" for everyone and her whole demeanor changed. Not to mention the "I feel wrong/気持ち悪い" line I translated the same for consistency.
Sayaka
Anyway what the fuck Sayaka. There's been a few hints she isn't totally clueless and knowingly bulldozes through her problems, back when she was relating to Michi in ch10. But this straight up suggests she knew Aizawa was a ghost this whole time, not to mention she knows Michi(?) made the AAA marks. I wonder if her policy isn't the opposite of Michi's: placating ghosts by acting like there's nothing unusual about them. It sure might work better with cases like Aizawa. And all her questioning about things like the mark on Michi's neck might be similar to how Karasuma felt out if Michi's memories were still gone, if she could level with her as a fellow spiritualist.
I still refuse to remove her handsome dumbass title but it's clear part of it's an act. Though I like that she doesn't really accomplish anything besides resetting the tone.
Seta
And Seta. Yes he has two moms. Back in chapter 6 there was actually a line implying this, "母ちゃんたちにわたすか/I'll give it to my moms." However I played it safe and translated it as mom singular. The thing about たち is it's an incredibly nondescript pluralization. You could say 瀬田たち to mean Seta+whoever, or in this case mom+whoever. I've gone back and adjusted the line, though it was much more vague in Japanese than English. Chapter 6 wasn't meant to be a big reveal but oh well. Just one of those language barrier things.
Other notes
Aizawa's chat icon is presumably a photo of her own cat, the one mentioned in the volume 2 extras. (It feels bizarre writing dialogue for her.) Also her cute/sad point to herself on page 14 when Michi tells Seta she has no friends.
On the bottom left of page 2 you can see what looks like Reona holding hands with another girl, the friend she mentioned last chapter. Side couple #2 coming soon.