Tsukumo Yamada is a completely average university student with no particularly redeeming qualities, going about his ordinary life on campus. The university is abuzz with talk of Mao Yoshida, a beautiful and solitary young woman rumored to be a mermaid princess who attracts the attention of nearly every male student. While the other boys make a loud fuss over her, Yoshida quietly beckons to Yamada. Once they are alone, her cold and aloof demeanor transforms into one of passion. In truth, Yamada and Yoshida are already in a secret and intimate relationship. They frequently meet in private, where Yoshida becomes much more dominant and demanding, needing Yamada to fully satisfy her before she is done. The central conflict for Yamada is his inability to understand where he truly stands with her. Because of her expressionless personality in public and their purely physical dynamic in private, he can never grasp the romantic distance between them and finds himself trapped in a sweet but bittersweet situation, unable to progress from being a friend with benefits to a true lover. The narrative follows this push-and-pull relationship as Yamada tries to figure out if his connection with the campus beauty can ever become a genuine romance or if he will forever remain unsure of her true feelings.