The three problem candidates were a swindler, a sadist who can only get off on hurting their partner, and a murderer. I thought Ida was the swindler, but now I feel like she might be the sadist. She wants to avoid the sex challenge and violence, not because she abhors those things, but because if she does either of them, her true self will come out. Plus, they said that the sadist retaliated against her abusive boyfriend when she learned to enjoy harming her partner, so that seems like that'll fit with her backstory.
Speaking of the swindler, I think Yamadasaki, the serious girl who did the schoolgirl roleplay, is the swindler. They said the swindler believes her own lies and can take on fake personas, so that fits Yamadasaki's acting abilities. I'm assuming Kumasaki is innocent since she's out early, so that leaves Shiori and Yuzuki as suspects for being the murderer. It's probably Shiori, but she's so suspicious, I feel like we'll be thrown a curveball and it's actually Yuzuki.