Iori Kitahara, a first-year mechanical engineering student at Izu University, enters college intent on an ordinary academic life until his uncle’s diving shop becomes his unexpected home. Coerced into joining the rambunctious Peek-a-Boo diving club, he confronts his fear of water and lack of swimming skills, eventually embracing diving as a transformative passion. His muscular physique, dark blue hair (varies in anime), and frequent shirtless or underwear-clad presence during the club’s alcohol-fueled escapades contrast his initially reserved demeanor.

Adapting to the club’s rowdy culture of heavy drinking and nudity, Iori balances chaotic antics with a compassionate core. He fiercely defends friends like Kouhei Imamura from mockery and stands by Aina Yoshiwara against bullying, while his perceptive empathy uncovers hidden struggles in peers like Sakurako Busujima’s pain or the Kotegawa family’s fractured communication. However, blunt remarks and occasional boundary-crossing behavior strain ties, particularly with disciplined cousin Chisa Kotegawa.

Family tensions shape his journey: younger sister Shiori resents his perceived irresponsibility for leaving her to manage their family inn, though he urges her to prioritize her own dreams. Relationships with cousins Nanaka and Chisa evolve from rocky beginnings—Nanaka treats him as a sibling while playfully nudging him toward Chisa, whose initial reunion with Iori is marred by his half-naked appearance. Gradually, he and Chisa forge trust, collaborating on tasks and staging a faux romance to deter her suitors. Their bond strengthens through shared diving adventures and emotional confrontations, such as untangling misunderstandings about Chisa’s mother, though romantic clarity remains elusive.

Growth emerges in his rising alcohol tolerance, boastful pride in drinking prowess, and selfless acts like risking his life to rescue Chisa from a cliff fall. A cringe-worthy song he composed in his music-obsessed past resurfaces when Shiori leaks it, morphing into a recurring gag. Beneath the chaos, maturity surfaces as he mediates conflicts—diffusing a lab crisis caused by a professor’s reckless assignment—and addresses interpersonal strife with earnest resolve.

Across official adaptations, including manga and live-action film, his narrative remains anchored in balancing club mayhem with personal evolution. While no spin-offs diverge substantially, his role consistently underscores adaptability, camaraderie, and incremental acceptance of responsibility beneath a comedic, carefree façade.