It's been a month since I moved into Room 505 of this housing complex, and I've finally finished unpacking and settling in. Today is my first day off in a while, so I'm lying down in the living room to relax when suddenly the door opens and an unfamiliar girl covered in mud walks in!

I can't make sense of the situation at all. As I stare dumbfounded, the girl who introduced herself as Yume-chan cheerfully reaches for the snacks on the table without asking and starts chatting in high spirits.