Aiichiro Nitori

First-year student at Samezuka Academy. In the second season, he is a second-year student, and in the third season, he is a third-year student. A member of the swim club who admires and looks up to Rin. He is 168 cm tall, weighs 55 kg → 57 kg, and was born on January 4th, making him a Capricorn. His hobbies include reading. His favorite foods are sandwiches and borscht, and he dislikes sour foods. He is hardworking and serious but has a unique fashion sense. He has a tear mole under his right eye. He admires Rin and dreams of swimming on the same team someday. In the drama CD, he often gets caught up with Captain Mikoshiba in Rin's antics, but after Momotaro joins, he ends up having to keep him in check.

During his elementary school days, he participated in the same tournament as Rin and Haruka, and has known them since then. His specialty was long-distance freestyle, but in the second season, he trained in breaststroke to swim in a relay with Rin. Although he was disappointed not to be selected for the relay team at the prefectural tournament, despite Momotaro being chosen, he achieved a personal best with Sousuke's help in breaststroke and was selected for the relay team at the regional tournament. When Sousuke revealed his shoulder injury, he sympathized with his desire to swim together. After Rin's retirement, he was appointed as the new captain.

In the third season, he competes in the national tournament. In the preliminaries, he races against Nagisa and wins. In the dormitory, he shared a room with Rin in his first year, but in his second year, the room assignments changed, and Momotaro became his roommate. He is not good at tidying up, and his desk is cluttered. He has a pet dog at home. His image is associated with a duck.