Ai is not satisfied with her husband's sexual activity, despite his earnest nature, and secretly feels unsatisfied. At that time, her brother-in-law, Bunta, suddenly comes to visit. Her playboy brother-in-law sees through her lewd Kokoro and skillfully seduces her... She is swayed by his sweet words and ends up having sex with him "just once". Although she refuses Bunta's persistent advances after that, the pleasure that shakes her whole body, which she could never experience with her husband, and the stimulation that gouges into her vaginal walls are intensely engraved on her body...