Mika's husband still has sexual desires, and they had sex again tonight. However, recently, they couldn't finish after the first time, and it was painful. She thought of exercising to relieve her arousal. She consulted her son, who agreed to give her a balance ball. That day, she was exercising on the balance ball, but her leg cramped up. Her son noticed and stretched Mika's leg. As he helped his mother stretch, he became aroused. Mika also began to feel strange when her son touched her. After he helped her stretch, her body was hot and she couldn't calm down. Mika started masturbating in secret. Her son found out...