Shiraishi Nagisa is a female college student who works as a cosplay idol and is her younger brother's girlfriend. When Nagisa comes to her brother's house to play, she shows off her sexy cosplay outfits, and just then her lawyer brother, Seiichi, comes home. Nagisa senses that Seiichi likes big breasts when he gives her a special look, and one day, by chance, she meets him on the street, and on the way, she rubs her big breasts against his elbow. This awakens the lewd side of the earnest Seiichi, who invites her to his room and has sex with her over her big breasts and cums inside her. Nagisa loves sex, and hides it from her brother and engages in titty fucking and cumming sex with her older brother, Seiichi.