快楽堕ちさせられる義妹・実奈美

The protagonist, Norikawa Kouta, lost his parents when he was young, so he was raised by his relatives alongside his cousin, Norikawa Minami. They grew up together like siblings, but as they became older, Kouta began to develop special feelings for Minami. He was aware that Minami thought of him as more than just a brother as well. However, he knew that his adoptive parents and the people around him would not accept their relationship, and he also thought that he would not be able to make Minami happy. And because of that, when it was time for him to enter university, he left home without telling Minami where he attended, deciding to cut off the feelings for his adoptive sister.

One year later, in the room of Kouta, who now lives in the city, Minami suddenly appears. She moves to the city in the spring in order to attend her university as well, she learns of Kouta's address and comes to visit him.