Mai is dissatisfied with her sex life with the man she is thinking of marrying. When her frustration reaches its peak, she ends up having a physical relationship with a kind man who attends her swimming class. She cheated on him just once...but before she knew it, her body began to desire a partner who wasn't him. At the end of the lesson, a beautiful instructor with a young, toned body, slender body, and outstanding figure loses herself in the empty pool and cries repeatedly.