Chisato's son loved his mother's big, round butt. At night when his father was away, he would masturbate while looking at his mother's butt, which was badly slept in. On the weekend, her husband, who was working away from home, returned home and the couple enjoyed a night of intimacy for the first time in a long while. Her son was secretly watching them. One day, his mother became concerned about her figure and started working out. As her son passed by, he was captivated by his mother's plump butt. Finally unable to hold back any longer, he attacked his mother's butt. "Mom, you shouldn't make your butt smaller..."