Yumi Kazama, 30 years old, is married to a middle-aged man much older than her... One day, her husband points out that she's gained a little weight since they first got married, so she decides to go on a diet! Watching her exercise, her stepson gradually becomes aroused by her young and beautiful mother, and indulges in his own fantasies. One day, he witnesses his stepmother's dissatisfaction with her sex life with her much older husband... At that moment, the stepson finally...