This is her first time living together with her boyfriend. Yui, who has always been dumped because of her caring and fatherly character, hopes to have a happy life this time around, but soon discovers that her boyfriend has been cheating on her. With no place to return to, she ends up in the messy room of Mizuo, a friend she has known since she was a child. They have always been together since childhood, and she thought she knew everything about him. However, Mizuo says in a low tone, "Don't ever come into my room," and leaves a meaningful message--? A chillingly sweet and crazy obsessive love that crosses the line between childhood friends--!