Recently, Mio and her husband have been feeling a decline in their physical strength. Their nighttime activities have also become dull. Mio has started doing light exercise and stretching to build up her physical strength. While stretching, she sees her son in the hallway. Mio calls her son and they stretch together. Her son gets an erection when he sees his mother bouncing on the balance ball. Mio notices that her son has an erection. That night, Mio cannot get her son's erection out of her head and masturbates in the kitchen. Her son sees this and...