Although their marriage is peaceful, Miki has been unsatisfied due to a long dry spell with her husband, leading her to relieve herself through masturbation. Her son, a serious and studious boy, accidentally catches her in the act. From that moment on, he begins fantasizing about his mother's lewd figure while masturbating. One day, Miki suddenly enters his room while he is pleasuring himself. Panicking, he shouts, "Don't just barge in!" But Miki retorts, "You're hard because of me, so you better take responsibility!" As their mutual frustrations collide, a forbidden relationship begins to unfold.