Mother Rena lives with her husband and their son Tsubasa. One day, Tsubasa unexpectedly invites a female friend over to study together. However, overwhelmed by desire upon seeing her, he ends up assaulting her right then and there. Learning of the incident, Rena is pained by her son's ignorance and innocence. Determined to guide him properly, she resolves to teach him about sex using her own body.