The mother, Leona, is summoned to school after her son, Seiji, has submitted a blank answer sheet for the health and physical education exam. Leona then realizes that Seiji still has no interest in sex and no knowledge of it. Later, when Seiji's classmate Issei learns of this, he proposes that Leona and herself have sex in front of Seiji. Leona is puzzled, but Seiji is threatened by Issei that he will be bullied, and she decides to have sex with him in front of her son.
