The protagonist has a childhood friend who grows up together with him named Kougami Yukimi. Although he has feelings for her, he never confesses, and then, Yukimi passes the entrance exam first and moves to the city.

A year later, he passes the exam as well, moves to Tokyo, and reunites with Yukimi. He then confesses his feelings, which he has been harbouring for over a year, and asks to go out with her. However, she refuses, telling him that even though she likes him, she cannot go out with him. When asking for the reason, Yukimi becomes reticent and does not give him a clear answer.

Nevertheless, he does not give up and continues to persuade her, and then, Yukimi suddenly asks him to have sex with her. Even though he is confused, he loses to his emotions and desires, and embraces her, but becomes confused even more, when he feels that Yukimi is experienced in blowjob and the cowgirl position.

After the act, Yukimi confesses that she has already had sex before and is no longer a virgin. Although he is shocked by the fact, he still asks her to go out with him, but she withholds the answer. Afterwards, their days of intimacy continue, and the protagonist assumes that they are already lovers.

Meanwhile, no, even before that, without the protagonist knowing, Yukimi has been doing a certain "job". And it is――