Natsume Takashi is a boy who has been able to see monsters since he was a child. Since he inherited the "Friends' Book" from his grandmother Reiko, a contract book that allows him to become a master and servant with monsters and write his name on it, he has been working with the monster cat teacher who calls himself a bodyguard to return names to monsters every day. Natsume meets various monsters and kind people, and while building a warm place, he also repeatedly places his thoughts on protecting important things.