Aiji-kun no 15-nen Himeta Shuuchaku-ai ga Fukasugiru.: Kawaii Osananajimi no, Kawaikunai Hodo Hageshii Koubi

Natsume Miyahara is an office worker who has been struggling with her sexual desires. When a coworker suggests trying a service for women, she casually mentions it to Aiji Kawai, her five-years-younger childhood friend and a popular nail artist. But Aiji, whom Natsume has always thought of as a cute younger brother, offers her another option: becoming intimate with him instead. As she begins to see the mature man he has become, Natsume realizes that Aiji has been hiding intense feelings for her for years. What she doesn't know is that his affection has grown into a deep possessiveness that he can no longer keep hidden. Their relationship takes an unexpected turn as her longtime childhood friend finally reveals just how strongly he has desired her.