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- Main article: Nagisa Hazuki
Nagisa seems to enjoy teasing Gou by calling her Gou instead of Kou, which is constantly upsetting her. Even though, the two seem to be on good terms and rarely fight (aside from him refusing to call her Kou). They often seen to have a same response, along with Rei.
- Main article: Haruka Nanase
In the first episode, Gou visited Haruka's house to ask him for information about her brother. She is also constantly swooning over Haruka and his figure. He is the only member of the Swim Club who recognizes her as Rin's sister and who Gou remembers.
- Main article: Makoto Tachibana
Makoto was the first one to notice Gou and the first one to actually realize that Gou is Rin's younger sister. Since the day Makoto and Nagisa ran into Gou in front of Haruka's house, all three of them started hanging out a lot and spending time together at school. After having a talk with Makoto at the school pool, Gou decided to join Iwatobi High School's Swim Club.
Unlike in Gou and Nagisa's relationship, Gou never gets angry with Makoto, despite him calling her "Gou-chan".
- Main article: Rei Ryugazaki
Gou's relationship with Rei is not greatly elaborated on in the series. They are on very friendly terms, as they see each other as friends. Their conversations seem to end with one of the party riled up: Rei's logical approach to life sometimes may clash with Gou's more irrational decisions and whims (he seems to be constantly exasperated with her obsession with muscles). Similarly, Gou seems to enjoy teasing Rei, calling him "stingy", calling him out on various occasions, and even asking him if he is the cause of the rain, which ends in Rei's flustered, angry yelling and her and Nagisa's laughter.
- Main article: Chigusa Hanamura
- Main article: Miho Amakata
It is unknown whether or not she's Gou's Classic Literature teacher as well as Makoto and Haruka's, but the two seem to have a friendly relationship. They act quite friendly towards each other and often do things together, bonding on swim trips and practices because they are the only females amongst the Iwatobi Swim Club. 
- Main article: Rin Matsuoka
Gou is often worried about her brother. One of her main reasons in becoming Iwatobi's swim manager is that the guys will help bring her brother back to normal. Rin in response appears a bit protective of her as well especially in response to Seijuro's use of Gou's first name and his attempts to go out with her, which are often ruined by Rin personally.
In the drama CD, Rin was curious about Gou who go out every Sunday, and thought that she goes on a date with Seijuro. He even called Makoto and asked him what are they doing on Sunday. After Rin and Nitori stalked Gou, they were suprised that Gou was actually helped by Hanamura to buy him a Christmas present, and that she wrote on the card "Thank you for everything, Onii-chan". Hanamura said that she's jelaous of Gou to have such a good-looking brother, but Gou aswered that he can be a pain sometimes and that he's never honest with his feelings.
- Main article: Seijuro Mikoshiba
Seijuro has a noticeable crush on Gou after their first meeting. He is always eager for opportunities to speak to her, shown by his enthusiastic acceptance of an idea of a joint swim practice with the Iwatobi swim team. Nevertheless, Gou is somewhat oblivious to his advances and attempts, as she always denies using her so-called "sex appeal" to hook the Iwatobi Swim Club up with Samezuka Academy for training. His attempts to go on a date with her are often thwarted by over-protective Rin. He usually calls her 'Gou-kun', adding boyish suffix "-kun" to her name, much to her dismay.
- Main article: Goro Sasabe
Gou's relationship with Goro is not greatly elaborated on in the series. However, they are on friendly terms.