It's very strange. I'm actually replaying from Chapter 2 right now trying to hammer down exactly when the shift happens, because she's still an innocent, naive girl and the reactions seem normal.
(Also, Ami shows absolutely no indication of being aware of time loops at this point so the chapter 4 reveal feels like a hamfisted retcon but this is just my opinion)
I’m doing the same thing: replaying the game from the start and taking notes specifically on the moments where Ami seems to show knowledge of the resets, moments where she clearly doesnt act like she has that knowledge, and moments where she might know but is maybe hiding it. And honestly, the possibilities I’m seeing are… fucking conflicting.
That said, I want to wait until I finish all of Chapter 2 before posting my full thoughts. It would probably be even better if I replayed the entire game first, but my notes are already getting pretty long and rambling. At least I’m about three-quarters of the way through Chapter 2 now.
From what i remember from the latest chapters, Sana has always been like that, she just didn’t have the self-confidence to act on her fantasies in the early chapters (because she really was fucking shy). She couldn’t bring herself to break socially imposed norms, at least not until she met Sensei, not so differently from Haruka.
Sana was also held back by the fear of becoming like her mother, an idea she despised, even though she takes after her 100%. And that’s not even mentioning everything involving her brother, the gods talking to her and her mom... there’s so much going on in her family.
Also Nodoka’s “sex radar” immediately pegged Sana as a total freak the moment she met her. Always trust in Nodoka.