Tsukumo Yamada is a simple and unremarkable college student. As he is getting ready to go home after finishing his university lecture as usual, a solitary, beautiful woman, Mao Yoshida, who is rumored to be a "mermaid princess," passes by. While the boys are in an uproar, Yamada is secretly summoned by Yoshida. When they are alone, Yoshida presses against him. In fact, Yamada and Yoshida have an intimate relationship. However, he is unable to grasp the romantic distance between them because Yoshida is too expressionless, and he is having a sweet but bittersweet college life, unable to go from "friend" to "lover".