H-ing with his girlfriend's busty, open and bold younger sister, Hajime, who has been dating her for a long time but still can't get her to have sex, finds himself inexplicably drawn to her. Despite his girlfriend's reluctance, Hajime is seduced by her younger sister's ample white breasts and open attitude, and quickly falls into a passionate affair. This is a story about a sleazy guy who gets lost in a cheating sexcapades with his girlfriend's younger sister, who's at the peak of her sexual desires.