#ymm

Tsubomi says, “I am able to awaken for a brief time while the other me is asleep.” Which could mean Mutsumi considering their hair is opposite of each other (one dark stripe vs. one light stripe). Could also mean that since this is Tsubomi’s consciousness talking that she can possess bodies but only for brief periods of time. Could also be relevant to wherever her heart is kept, depending on if Momo is literally keeping Rei’s heart in that suitcase of his. Lots of options of how to interpret what she’s implying here. I’m leaning towards it being Mutsumi

As I suspected, something about Tsubomi is indeed keeping her alive in some way. It’s also possible that her soul is bound to that book of hers, but I would think it’s likely going to be deeper than that. Which turns out to be true as I read on because Kawashita has some kind of relevant information, so you can’t kill Tsubomi using only her book.