Housewife Toka lives with her husband and her daughter's family, making four people in total. Ever since she became pregnant with her daughter at a young age, her life has been consumed by child-rearing, causing her intimacy with her husband to dwindle. Her pent-up desires and neglected body begin to draw the attention of her son-in-law, Kōhei. Overwhelmed by her stunning beauty and obscenely large, seductive breasts—qualities that make it hard to see her as just a stepmother—Kōhei's restraint crumbles, leading him into an illicit affair within the household. Unable to resist, he moves closer to Toka, pressing his advances upon her. Though Toka resists wholeheartedly, crying, "No, I can't... he's like a son to me!", she gradually succumbs to her son-in-law's intense sexual desire, her emotions and resolve beginning to waver.