Yumi, married to a man with a son, has always been loved by her stepson Ryo since they first met. As Ryo began to see Yumi as a woman, he started pulling away from her. Wanting to deepen their relationship even more, Yumi takes extra care of him... until one day when she catches Ryo masturbating while smelling her underwear. Surprised yet aroused, Yumi asks if he wants to learn how to kiss like an adult.