MCbro finds out that the demons are manifestations of Mai's psychic powers, caused by her sadness over not being able to continue seeing him after he moves away. Mai promises that they and Sayuri will live together after they graduate, then she just stabs herself and dies in his arms. It then flashes back to when she discovered her powers, then cuts to her meeting MCbro for the first time, and she says that she's been waiting for him and hope he never leaves. It then shows Mai and Sayuri's graduation and MCbro moving in with them, despite that directly contradicting the fact that she just died.

My interpretation is that she somehow created an alternate timeline where he never moved away by killing herself, or that MC had similar powers and revived her by crying. Either way, it didn't make a lot of sense and felt really forced.

people being reborn and second chances, in the VN's case, I think Yuuichi's love brought her back. I thought the 2006 anime had a similar scenario of her being revived, or she simply self-healed after that demon revelation.