Yumi, an education-oriented mom who is enthusiastic about enrolling her son, Yosuke, in the same prestigious school as her husband. She has no flaws at all, but her body becomes sensitive only once a month on a dangerous day, and her estrus becomes uncontrollable. Yosuke secretly finds out about her, and pretends to be a coincidence to relieve her daily frustration and shows him masturbating on a dangerous day... Her husband was on a business trip and hadn't had sex in a long time.
