Aiichirō Nitori is a student at Samezuka Academy, a school known for its competitive swimming program. He enters as a first-year and progresses through to his third year, eventually becoming the captain of the Samezuka Swimming Club. After high school, he continues his education and swimming career at Shimogami University. He was born on January 4. He has light blue eyes and short, straight gray hair, with a distinctive beauty mark located diagonally below his right eye. Standing at 168 centimeters during his early high school years, he later grows to 171 centimeters and is generally the shortest member of his swim team. His initial interest in swimming was sparked during an elementary school competition where he witnessed a relay race involving Rin Matsuoka. Although his own team lost in the preliminaries, he was deeply moved by Rin’s performance and has admired him ever since. He is friendly, earnest, and a dedicated hard worker who participates enthusiastically in club activities. He is also somewhat chatty and can be prone to saying too much at inappropriate moments, yet he is not easily discouraged by a harsh word or cold glare. Despite his bubbly and cheerful nature, he is prone to nervousness and shyness, and he is emotionally open, easily moved to tears by both happy and sad situations. He has a scatterbrained side, evidenced by his perpetually untidy desk. His primary motivation is his deep admiration for Rin Matsuoka, whom he looks up to as a mentor and role model. Wanting to be like Rin, who excels in multiple swimming styles, he decides to specialize in both freestyle and breaststroke, with the goal of earning a place on the medley relay team alongside Rin. When he struggles to improve, he receives crucial coaching and encouragement from Sōsuke Yamazaki. With this help and his own perseverance, he successfully improves his breaststroke time, earning his spot on the relay team. At the end of his third year, Rin appoints him as the new captain of Samezuka. He is Rin’s underclassman and roommate, later rooming with Momotaro Mikoshiba, and his relationship with Rin evolves to the point where Rin calls him by his first name, “Ai.” He has a fondness for cute things and a distinct fashion sense. As a swimmer, he specializes in long-distance freestyle and breaststroke, and he has a personal ritual of putting his right leg into his swimsuit first for good luck. He keeps a preserved umbilical cord and childhood journals, and his hobbies include reading and playing with his dog. He favors borscht and sandwiches but dislikes sour foods like pickled plums.