Mako Oda lives with her remarried husband and his stepson. Though her married life lacks major complaints, she finds herself living a dull and unstimulating daily routine. Her husband is more absorbed in work and smoking than in their relationship, leaving Mako feeling deeply lonely. One day, overwhelmed by this loneliness, she begins masturbating intensely to find release. By chance, her stepson catches her in the act. From that moment on, she starts secretly craving creampie sex, careful not to let her husband notice. Gradually, consumed by her growing sexual desires, her behavior begins to change—under the watchful eyes of her stepson, her transformation unfolds.