A cool boy, opposite of his younger brother. He doesn’t try to stop anything his brother does, always watching over him instead. A boy who loves to sleep, Mutsuki does things at his own pace. He used to have a weak constitution, so he didn't have playmates aside from Satsuki. Because of that, he has a habit of drawing a line between himself and people that he interacts with. Despite that, he has grown fond of Futami.
