Crystalia
A highschool boy, Getsuma, doesn't like your family that much was walking around, and in one of your way to home, he meet up to 2 strangers: one a girl who says to him remember her name, and other tall boy that has scary look that is always on side of girl. Getsuma runs away from weirdos since he doesn't have any idea who are them, but when he gets on his house, they're already there and right after his mom says that those 2 will be living on same roof.
Text based series will tell supernatural adventures about this strange encounter, is what Getsuma has forgotten is related to things that are going to happen on story?