On an evening disco dance held by the students at Tomobiki High School during summer break, Class 2B's teacher, Onsen-Mark, warns the students of a demonic and enigmatic man known as the 'Red Mantle' notorious for the abduction of one of Onsen's own peers. Upon the night of the dance, however, the Mantle himself is revealed to be an overweight and incompetent has-been, obstructing his 'schemes'.