Movie
Description
Aiichirou Nitori is a student at Samezuka Academy and a member of its prestigious swimming club, later becoming its captain during his third year. He has light blue eyes and short gray hair with straight bangs, a style the character designer chose to give him a distinct "cute" feeling without conflicting with other characters' designs. A notable feature is a beauty mark located diagonally under his right eye. His height is initially 168 centimeters, later growing to 171 centimeters.

Nitori first encountered Rin Matsuoka and the other main characters during an elementary school swimming competition. Although his own team lost in the preliminaries, he was deeply moved by watching the winning relay race that included Rin, Haruka Nanase, Makoto Tachibana, and Nagisa Hazuki. From that moment, he began to look up to Rin. This early exposure to their talent and teamwork shaped his desire to one day be part of a similar kind of relay team.

His personality is friendly and earnest, though he can be somewhat chatty and occasionally says more than he should. He is a hardworking swimmer who is very aware of his own limitations, which sometimes leads him to push himself to extremes in an effort to improve. Despite being snapped at or brushed aside by Rin, Nitori remains loyal, cheerful, and never gives up. His admiration for Rin is so strong that he initially tries to specialize in two swimming styles, just like his role model. He has a habit of keeping a diary in which Rin is mentioned on nearly every page. In his first year, he shares a dorm room with Rin, and his desk is often untidy, much to Rin's annoyance.

Nitori's role in the story is primarily as a supportive underclassman who helps draw out Rin's character. The director of the series noted that Nitori was created to be a conversation partner for Rin, a character who would not be discouraged by Rin's hard-heartedness and would help prevent him from becoming isolated. Nitori cares deeply for Rin and feels sincere happiness for his victories. At one point, he feels miserable about being unable to participate in his preferred event, which initially prevents him from understanding why Rin, who could compete in any event, chooses only the hundred-meter freestyle.

His key relationships center on his fellow members of the Samezuka swimming club. He looks up to Rin Matsuoka as a mentor and role model, faithfully supporting him and trying to emulate his techniques. He also develops a significant relationship with Sousuke Yamazaki, a talented transfer student and Rin's childhood friend. Although Sousuke first seems cold toward him, he later offers to train Nitori personally, helping him improve his breaststroke. Nitori greatly admires Sousuke for both his skill as a swimmer and his long history with Rin. He interacts with the Iwatobi Swim Club as well, especially Nagisa Hazuki, who gives him the nickname "Ai-chan." His dynamic with Nagisa is friendly and competitive, particularly when they face each other in races.

Nitori undergoes notable development as he learns to overcome his self-doubt. He initially believes that swimming ability is determined by natural talent and that his own efforts are futile. After being surpassed by a younger teammate, he struggles with the feeling that he is wasting his last summer for a chance to be on a relay team with Rin. With encouragement and training from Sousuke, he learns not to deny his own potential. His hard work pays off when he achieves a personal best in the breaststroke and earns a spot on the relay team for the regional tournament. By the end of his third year, Rin appoints him as the next captain of the Samezuka Swimming Club, recognizing his dedication and growth.

In terms of abilities, Nitori initially specializes in long-distance freestyle. However, he trains extensively to master the breaststroke so he can join Rin in a medley relay. He is a dedicated and consistent worker who practices early in the morning and puts in extra time on his own. While he is not portrayed as a natural prodigy like some of his peers, his persistence and willingness to be coached allow him to achieve significant improvements. He eventually competes in the national tournament, where he wins his heat in the breaststroke.