Arata Tatsumi is an honor student who happened to witness another freshman student like him having sex with a female senior in the library.

All he could think about since then was that senior girl. When he tries asking Aizawa, the female senior from that time, what she was doing back then after school when he was studying in the library, she readily admits that she's having sex regularly at that time.

When he tells her honestly that he's envious, he ends up being given a special chance where she'll listen to "anything" he wishes from her...

(Source: DLsite garumani, translated)