The setting takes place in a small country town. Lately, there have been strange things happening there. Along comes the monster-like kindergartner "O-O-O-No Shinnosuke" and his father, the monster "Accidental Dad." They are looking for their mother who ran away from home, the monster "Big Butt Hag."

Shinnosuke saves the town girl, Fumie Sakura, who is attacked by mysterious monsters which suddenly appear. Their meeting is the start of a small town's grand monster case.