So my theorist mind has been buzzing recently, and last night, I came up with a sort of sequel to my previous one about Natsuki knowing everything.

I think it wasn't just Natsuki.

I think all the girls knew what was happening, but had agreed to go along with the script for fear of breaking the immersion, or denying the player the world they wanted to become a part of. Whilst this sounded great to Sayori, Natsuki and Yuri, this still left Monika to watch on the sidelines.

When Sayori got MC to join the club, Natsuki was rude to him because she was afraid that the inclusion of a connection to the real world would be enough to temp Monika into ruining the game, but it doesn't work, since MC joins no matter what. This explains why Sayori has never seen Natsuki and Yuri fight so aggressively before.

Then, Sayori hangs herself at the end of act 1, the game resets and this is where things begin to make a little more sense from this theory's point of view.

I based this on the fact that when I played through the game again last night in an attempt to get the good ending, I decided to take the Yuri route this time instead of trying and failing to spend time with Natsuki. On multiple occasions before Yuri's obsessive traits reach their peak, she manages to stop her self and be like "What's happening to me?" and "I'm not normally like this." This means she knows something is wrong, she just can't be sure if it's Monika.

As for Act 2 Natsuki, if she was able to alter herself, just with nothing long-lasting, then that explains why Monika says that she didn't touch Natsuki's file all that much in your extended conversation with her. That part where she snaps her neck? That was Natsuki's own doing. She wanted to make herself undesirable so that Monika wouldn't tamper with her in a way that would leave a lasting mark.

However, despite their efforts, nothing works. Yuri's obsession with MC becomes to great for her to reign herself in, and she ends up confessing. We all know where thing go after that.

This theory, I suppose, picks up again in act 4, as no particular points in act 3 are relevant other than perhaps Monika's note about Natsuki's file, but we already mentioned that. Anyway, it doesn't matter if you get the good ending or the bad ending here, Sayori gains sentience for the ending, is what we're lead to believe. However, she never explicitly states that she never knew she was in a game. She just says "I understand now..." or "I know what Monika did." Which she couldn't have known until she was reinstated into the game in act 4. She didn't only just realise what her reality was, but rather what happened to it.

Phew! You got all that? Good, think about it like that for a moment!