Yui Nanase, 29 years old, is married to a middle-aged man much older than her. One day, Yui decides to go on a diet! Watching Yui working out, her stepson gradually becomes aroused by her young and beautiful stepmother, and indulges in selfish fantasies. One day, the stepson witnesses his stepmother's dissatisfaction with her sex life with her much older husband in real life. At that moment, he finally...