Aiichirou Nitori is a student at Samezuka Academy, an all-boys school known for its powerful swimming team. He has short gray hair, light blue eyes, and a distinctive tear-shaped mole diagonally under his right eye. Standing 168 centimeters tall as a first-year, he grows to 171 centimeters by his final year. Born on January 4th, his zodiac sign is Capricorn. Friendly and earnest, Nitori is often a chatterbox who can speak without thinking, yet his intentions are kind. He struggles with self‑confidence, acutely aware that he lacks the natural talent of some teammates, but he is also extraordinarily hardworking and persistent. His defining motivation is his deep admiration for Rin Matsuoka, which began in elementary school when he witnessed Rin compete in a relay. Nitori’s ultimate goal is to swim on a relay team with Rin. To achieve this, he masters both freestyle and breaststroke, emulating Rin’s versatility. With guidance from senior Sousuke Yamazaki, who helps refine his breaststroke technique, Nitori overcomes his self‑doubt, breaks the school’s breaststroke record, and earns his place on the regional relay team. He shares a roommate bond first with Rin and later with the energetic Momotarou Mikoshiba, often serving as a calm foil to Momo. He develops a friendly rivalry with Nagisa Hazuki of Iwatobi High School. After Rin’s graduation, Nitori becomes the captain of the Samezuka Academy Swimming Club. It is also revealed that his mother’s relative is Mikhail Makarovich, a coach who works with Rin, making the coach his uncle. Outside of swimming, Nitori has an untidy desk, keeps unusual items like his preserved umbilical cord and a childhood journal, enjoys playing with dogs, and likes borscht. After high school, he enrolls at Shimogami University.