Leona, a mother, is called to school after her son Seiji turns in a blank exam paper for health and physical education. Leona then realizes that Seiji still has no interest in sex and no knowledge about it. Later, Seiji's classmate Kazukiyo finds out about this and suggests that she and Leona have sex in front of Seiji. Leona is hesitant, but Kazukiyo threatens her by saying that Seiji will be bullied if things continue as they are, so she decides to have sex with Kazukiyo in front of her son.