A high school student named Kaoru Hanai develops an intense infatuation with a girl named Sonoko, who is a leading member of his school's swimming club. This sudden romantic interest serves as the primary catalyst for his actions throughout the story.

Driven by the desire to win Sonoko's heart, Kaoru decides to join the very swimming club she leads. This decision is made despite a significant personal obstacle, as he does not know how to swim at all. His determination to be close to her compels him to confront his own limitations, particularly his inability to swim and an accompanying fear of the water. This endeavor becomes a central part of his character, as he dedicates himself to mastering a skill for which he has no natural aptitude.

Kaoru's personality is largely defined by his singular focus and persistence. He is portrayed as someone who, once he sets his mind on a goal, pursues it with unwavering dedication, even when the odds are against him. Although his motivation is romantic, his approach is often described as a personal quest, setting himself the lofty ambition of becoming an Olympic swimmer to impress his love interest. This delusion of grandeur is part of his charm, representing a naive but earnest devotion.

In the context of the story, Kaoru’s role is that of a determined newcomer. Despite his lack of skill, he trains hard, yet he remains one of the weakest members of the club. His journey is not a typical underdog sports story; he does not achieve triumphant sporting success. Instead, his narrative focuses on the personal growth that comes from pursuing an unattainable goal.

Regarding key relationships, his interactions are centered around a few individuals. Sonoko is the primary object of his affection, but she remains distant and somewhat cold toward him, fitting a classic pattern where the pursued character is not immediately receptive. He has a friend named Pu, who lends him a motorcycle that Kaoru uses in his attempts to impress Sonoko; notably, Pu appears to harbor romantic feelings for Kaoru herself, creating an unrequited dynamic within his own circle. He also finds an unexpected ally in Sonoko’s mother, who assists him in his romantic endeavors, as well as a quirky older woman who acts as his swimming coach.

In terms of development, Kaoru’s arc does not culminate in him winning the girl or a major competition. Rather, his growth is defined by the realization of his own limits. He eventually learns that his persistent pursuit may be causing more harm than good, leading him to reconsider his actions and the impact they have on Sonoko. He learns to swim and makes progress, but his lingering fear of the water remains, and he ultimately stops short of the traditional happy ending, suggesting a maturation beyond his initial infatuation.

Notably, Kaoru Hanai possesses no superhuman or unique abilities. His most defining trait is his sheer determination and willingness to face his fears. Aside from his romantic drive, he does not demonstrate any exceptional physical or intellectual skills.