Reiko Shimura is a married woman living comfortably with her husband, Kenzo, the president of a construction company, and their only son, Kosuke. Despite her seemingly perfect life, Reiko harbors one deep dissatisfaction—her unsatisfying sex life with her arrogant husband. As a dominant, sexually assertive woman, she finds no compatibility with her passive husband, and they haven't had sex in over ten years. One day, Reiko meets a submissive man (M-man) through a dating site and finally indulges in passionate intimacy again. When her husband discovers the affair, he punishes her by enforcing strict sexual abstinence. Desperate and craving release, Reiko turns her attention to her only son, Kosuke. How their relationship evolves—and what Reiko truly desires—marks the beginning of this forbidden story of incest.