Koichi, who can't help but be curious about his busty, beautiful stepmother Sumire, approaches Sumire when his father is not around. Recently, Sumire has been frustrated by her father's busy work, and when Koichi touches her breasts, she feels sensitive! ! Koichi is fascinated by Sumire's big breasts, and he can't contain his excitement and ends up having sex with his stepmother... Since then, the two continue their relationship behind his father's back, and become immersed in a forbidden relationship.