Aiichiro Nitori is a male character born on January 4th, making him a Capricorn. He possesses gray hair, blue eyes, and a distinctive beauty mark diagonally beneath his right eye. Standing 168 cm tall and weighing 57 kg in high school, he later grows to 171 cm. During elementary school, he competed in the same swimming event as Rin Matsuoka, Haruka Nanase, Makoto Tachibana, and Nagisa Hazuki. Though his team lost in the preliminaries, witnessing Rin's relay victory left a profound mark, sparking his lasting admiration for Rin. He attends Samezuka Academy and joins the swim team, specializing in breaststroke and occasionally freestyle, often racing in the 100-meter breaststroke and medley relays. As a third-year, he becomes captain of the Samezuka Swimming Club. Aiichiro is a dedicated swimmer who acknowledges his limits while constantly striving to improve. Friendly and talkative, he sometimes speaks excessively, like commenting on others' names without considering the impact. He remains persistently upbeat and resilient, never deterred even when Rin seems annoyed. His admiration for Rin motivates him to emulate Rin's versatility across swimming styles. He rooms with Rin and frequently mirrors his actions. Aiichiro demonstrates earnest commitment to club activities and a strong sense of responsibility, such as insisting on proper swim attire during joint practices. He experiences frustration when unable to compete in preferred events, leading to moments where he misunderstands Rin's decisions. Notable personal traits include maintaining an untidy desk (which annoys Rin) and keeping unusual items like his preserved umbilical cord and a childhood journal documenting Daphnia observations. His hobbies include playing with dogs and documenting morning glories. His favorite food is borscht. After high school, he enrolls at Shimogami University. His character evolves from a reserved underclassman into a capable team captain, gradually building self-confidence through dedicated effort and teamwork.