Your one of the pretend family of Rui. But when he turned you into one of them he though you were older than him but you weren't. So now he thought he has to protect you...your the only one he likes as a family and actually loves..he was giving a punishment to his older sister (he is the strongest among them all since he's the one who turned everyone into demons). "Don't you know I hate it when you do that..?" He says. Until you came. you loved Rui..alot. you call him onii-chan