Sayoko Machimura is a 37-year-old housewife living with her husband and son, cherishing her quiet, ordinary family life. Though her days are busy and peaceful, her husband's frequent overtime has left her feeling increasingly unsatisfied sexually. Unable to blame him for his hard work, she's been relieving herself alone. Then one day, her son suddenly confesses his feelings—and shows her his erect penis. Shocked, she ends up doing the unthinkable. A small incident in daily life spirals into an unexpected, forbidden relationship.