The concept is quite dangerous. I've seen a lot lately manga taking concepts that lead to doujin hentai, ntr.
But this one is strange and intriguing and different. I like the main character who is aware but not too self-conscious in his wild fantasies. Not pervy or disgusting at all. Like, almost all time he will says, "There is a girl in my room!" "Oh, shit." this is acceptable because there are humane considerations.
The way we know the main female lead is also interesting, over time her skin peeling off and exposed to the tragedy that befell her.
As a depressed person I think I can understand her feelings of being interested in related "dark" matters. Usually it's about why we live in the world, what is death for us, what purpose --everything that makes us question existence (I have an episode but I'm still living normally which is more like panic and feeling overwhelming, so it's kind of struggle) and also interested in reading philosophy in self-acceptance. It won't be easy...