Yuki is married to a man with a child from a previous relationship, living day to day—but recently she's become self-conscious about gaining a little weight. As she diligently exercises in a leotard gifted by her husband, she begins sensing something different about her stepson's behavior, an odd atmosphere surrounding him. Her teenage stepson can't help but be captivated by the sway of her mature body, his mind consumed with lustful fantasies. One day, Yuki asks her stepson to assist her with her workout routine. In that moment, an entirely new and unexpected development begins.