Mari lives with her husband and son. Her son's hobby is spying on his parents' nighttime activities and masturbating to them. One day, Mari goes to her room to call her son. When she opens the door, she finds her son masturbating. Her son is sulking, saying, "It's the worst thing to be seen by your parents." When she tries to convince him that "masturbation is not something to be ashamed of," her son demands that she show him how she masturbates. From that day on, Mari is unable to stop her relationship with her son. She becomes addicted to the forbidden pleasures she shares with her son...