Stepmother Satomi has feelings for her shy and quiet son Ryota that go beyond those of a mother. One day, Ryota invites his friend Daisuke over to their home. Satomi is happy, but Daisuke sees her masturbating in the living room while calling out Ryota's name, and he threatens her into submission. Satomi continues to do as Daisuke says, demanding her body, and she becomes his sex slave.