Find your tribe in a Sea of Creativity
Okay here is my theory in short after the (festival) Watanagashi we don't meat Mion we only ever interact w Shion.(I'm at the very begining of Meakashi rn like ch 1)
Let me explain Mion never really comes to or stays for long in school afterwards but when she interacta w Keiichi it feels very different than before (might be related to the doll incident but I don't think that's it) she has that in my opinion very Shion like edg to her that somewhat vindictive/bitch way to it PSA: I don't think Shion is evil she just kind of has that feel to her character. It just kind of feels like none of the heartfelt moments betwen her and Keiichi never happened which would also make sense if it was Shion bc those things she wasn't present for.
About the phone calls: Shion never gives us her number which would make sense if she was for some reason calling from Mion's house which is in a school registry of some sorts idk kind of sus but not really damming evidance.
About Oryo or the "hag" (I love Shion can you tell she is soooo ahhhhhh love her so far) murder now more than ever makes more sense for Shion she hated her so damm much its not hard to see if she was pushed by circumstance (like Keiichi in Tatarigoroshi w Teppei) she would commit it even Satoko's and Rika's murder would make more sense w Shion neighter of them was she particularly close to as far as we know in the story.
And my last bit of evidance basment "Shion" never confirms who she is before dying (the person in the "basment"). And "Mion" (Shion in this theory) pretends to be her self again taken by the police and let go goes to Keiichi's house and stabs him when he comes out (idiot she told she'd be dead and only a demon would take her place but what ever) then goes back to her apartman falls down and dies. So yes everything can and does still work.
Is this a metric fuck ton of reaching yes but I had fun thinking about this and I'd be dammed if I didn't write this out of me. That's it thanks for reading my deranged rambelings I truly lost my way....I think.