The Prickly Little Sister with the Perfect Breasts... I Want to Win Her Over and Make Her Fall for Me! Due to his parents’ circumstances, the protagonist lives alone with his younger sister, Haruka. At ●●, she is the “Student Council Discipline Committee Chair,” a position even her teachers respect. On the other hand, he has a side to him as a breast fetishist and a cosplay enthusiast (the type who makes others cosplay), and although he hides it thoroughly, his room at home is lined with a full collection of cosplay outfits. At home, Haruka despises her brother for his completely different, perverted side, and outside of that, she often swears at him or even gets physical. One day, while cleaning, Haruka discovers a tissue used for masturbation in the trash her brother had thrown out. Despite her disgust, her curiosity gets the better of her and she sniffs it—unconsciously arousing herself just a little. The protagonist witnesses this, and, thinking that his sister might be aroused by the scent of semen, decides to use this weakness against her to make her listen to him a little more. And so... he sets out to turn her into an obedient, sexy, and cute little sister.

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