A 3rd-year student at Samezuka Academy, 179cm tall. He has a younger sister, Matsuoka Gou. His hobbies include muscle training and running while listening to music. He excels at sports that use his legs, and his main event is freestyle. He is a childhood friend of Haruka's group and Haruka's rival. Aiming to become an Olympic representative, he left for Australia to study swimming abroad around the time he entered middle school. As a child, he was sociable and friendly, even approaching the blunt Haruka first, but after returning from his studies in his second year of high school, he became cold and prickly, baffling Gou and his old teammates. Among the characters, he is the most combative, obsessed with winning, and has a strong selfish streak. After resolving his conflict with Haruka, his personality softened, returning to his old caring self. However, his competitive spirit remains; he vows to heat things up in a match against Haruka at a citizens' meet or taunts Rei during a butterfly match not to get bitten. Unlike before his reconciliation with Haru, this energy is now expressed in a positive way. Since he moved into the Samezuka Academy dormitory immediately after returning from Australia, he does not live with his family. He has a habit of snapping the back of his goggles when psyching himself up, a habit since childhood. Despite his rough speech, he is a handsome character who is flexible in his actions. He might look lighthearted on the outside, but he is surprisingly serious. According to High Speed!, he is the hard-working type whose success comes more from effort than raw talent.

A 3rd-year student at Iwatobi High School. He loves mackerel. His main event is freestyle. While Makoto, Nagisa, and Rin are all childhood friends, only Makoto went to the same middle school as Haruka, so Makoto is the only one he stayed in constant contact with until high school. However, Nagisa, who is one year younger, followed Haruka and Makoto to Iwatobi High School. He loves swimming and has a unique philosophy regarding water. He will strip and jump in the moment he sees water (even a fish tank at a supermarket) and is easily lured by Makoto's talk of swimming pools, even into bothersome situations. He dislikes people who hate water, but quickly shows favor to those who try hard to swim even if they are bad at it, sometimes even teaching them. His expression is usually a blank face showing no emotion. His swimming, which makes one feel a calm yet powerful energy, has fascinated many. Perhaps because of this, anyone in Iwatobi who has swam knows Haruka from his elementary school days. He is so stubbornly committed to swimming freestyle that he says, "I only swim free." His skill seems to transcend mere talent; he even defeated Rin, who had studied abroad specifically to become a professional.

A 2nd-year student at Iwatobi High School. His main event is breaststroke. He followed Haruka to the same high school. Even if others are older than him, he doesn't mind and speaks casually. Nagisa's enrollment at Iwatobi High was the catalyst for everything: he convinced Haruka to go to the swimming club building and Samezuka Academy to meet Rin, he took the lead in forming the swim club, and he recruited Rei, completing the team. His contribution is immense. His hair looks blonde but is officially light brown. His eye color was set to pink to emphasize cuteness, and it's fun because he looks good in any bright color or outfit. He is honest, direct, and doesn't hesitate in his speech or actions. He has a strong 'my pace' temperament. He is one of the gutsier members; unlike the fearful Makoto, he is fearless and likes horror movies and bugs. Longing for Haruka's swimming and wanting to swim together again, he entered Iwatobi High where Haruka was. Upon finding out there was no swim club, he discovered the old pool was still there and pushed the idea of starting a club. He acts on instinct but isn't stupid; he has a shrewd side. He is more strong-willed than he looks and shows a thorough side, though he occasionally acts like a klutz. For example, he brought sugar instead of salt to sprinkle on Makoto for purification, or he jumped naked into the Samezuka Academy pool facilities just because he wanted to swim. He has a feminine-sounding name.

A 3rd-year student at Iwatobi High School. His main event is backstroke. He is kind and considerate, but has a fearful and timid side. He is the sweet, boyfriend-like type who takes good care of others. His swimming style is power-based, showing a masculine charm that proves he isn't just soft and gentle. Contrary to his gentle impression with drooping eyes, he is the most muscular character in the group.

A 2nd-year student at Iwatobi High School and the manager of the swim club. She has a ponytail and looks a lot like her older brother; she is frequently mentioned as a beauty in the series. She joined the swim club, but unlike her brother, she doesn't seem to be good at sports, including swimming, so she serves as the manager. She is also a hardcore muscle enthusiast.