Housewife Mirei lives with her husband and their daughter's husband, Yoharu, in a four-person household. Though her days seemed ordinary, her marital intimacy had grown distant, leading her to engage in an affair. One day, she accidentally discovers a video starring Yoharu at a love hotel. Confronting him about it—believing he might be cheating on her daughter—she instead has her own infidelity exposed. Taking advantage, Yoharu boldly suggests, "If you want to have an affair, why not have it with me?" Using his young, hard cock, he aggressively seduces her. Despite being his stepmother, Mirei's stunning beauty and obscenely large tits drive Yoharu into a frenzy of lust. Unable to resist, the two plunge into a taboo, incestuous affair within the household, consumed by creampie-filled encounters and forbidden desire.