Original title: ビッチ姉ちゃんが清純なはずがないっ！
Ebina Tsukushi was just a normal high school guy who didn't stand out in his class at all.He wished that - despite being distanced from his childhood friend Fujikawa Himawari - he would have hope for his love life in the future.
But even when he tried inviting her to walk together from school, she only told him that "It would be embarrassing if there was rumors spread about us being close," slightly crumbling his heart. Even when he confessed to her, he got utterly shot down and became very depressed.
However, on that same day he got rejected, his very confident and popular older sister Nadeshiko, who had been studying abroad, returned home!
Wanting to be as confident as she was and live a fulfilling high school life, Nadeshiko, who was also huge brocon, just told him: "Leave it all to me!" A couple of days later, he found out that she had planned something up together with the school's haraguro nurse, Ayame --
With the power of his big and powerful cock, he would conquer the hearts of his schoolmates (including a teacher's) and create himself a harem. With the help of both Nadeshiko and Ayame, Tsukushi's unexpected harem life began!