Marina and Rena are good friends who are mothers. One day, while having a tea party as usual, the topic turned to sex life. Rena seems to be having a fulfilling sex life with a young man she met on an app, and half-forcefully recommends the app to the shy Marina, saying "Just once".... Shinji, a student she met on the app, is a cute boy who is obedient and honest. Marina awakens to the pleasure of dominating younger men, and gradually, Kokoro and body become addicted to dangerous play with younger men.