Kazuyo is a housewife who has become obsessed with working out after starting a diet, bringing her body fat percentage down to 20%. However, her husband barely pays attention to her, leaving her emotional and physical desires unfulfilled. One day, she's approached by a gym acquaintance named Maeda, and they begin an affair. Then, during a workout session with her son Shoji, an unexpected and taboo relationship begins to unfold.