Trying to relieve her lack of exercise, Honoka decides to try working out indoors with her husband. Watching her shake her hips on a balance ball, her husband can't resist, strips off her clothes, and starts caressing her. Their son accidentally witnesses the scene and becomes captivated by his mother's body, starting to masturbate. One day, Honoka catches her son in the act and realizes he's been using her as masturbation material—gradually, she grows aroused. Unable to hold back any longer, she finally gives in herself...