|“||Don't call me Gou!||”|
— Gou, speaking to Nagisa Hazuki.
|Also known as||Kou (Kō)|
|Occupation||1st year High School Student|
|Affiliation|| Iwatobi High School|
|Relatives|| Father (deceased)|
Rin Matsuoka (brother)
|Light Novel||Chapter 6|
Her usual school uniform consists of light brown skirt, white shirt with red bow tie, light gray long sleeved jumper, dark gray unbuttoned blazer, blue socks and black shoes. During the spring and summer, she would wear her summer uniform, which consists of gray skirt, white shirt with dark gray collar, red dotted bow tie, light gray sleeveless jumper, white socks and pink shoes.
Gou has an easygoing and refreshing personality, as shown by the way she talks. However, despite her friendly persona, she can get very angry if someone were to call her "Gou" because it is a rather boyish name for a girl. She prefers being called "Kou" and will always try to correct anyone who chooses to call her otherwise. Nagisa calls her "Gou," despite her constantly trying to correct him.
Gou also seems to be worried about her brother Rin a lot, as she regularly and persistently checks up on him and sees to it that he is all right. She even opted to be the Iwatobi Swim Team's manager, so that they could help in changing Rin back to his old self.
As a manager, Gou can be strict when needed, but at the same time, supportive of the swim team's decisions and feats. She is actually quite efficient in her role as manager and often makes the effort to improve on their training by setting up the team's regimen and organizing joint swimming practices.
Gou has an odd tendency to blush and get overly enthusiastic whenever she admires the muscles of men.
Gou's father was a fisherman who died in a fishing boat when she was very young. She appears to have been born in Iwatobi, and to have moved a short time afterward to another school district. Around the age of ten, her grandmother died and Gou, Rin, and their mother inherit the house in Iwatobi where her grandmother lived. At this time, she and her mother become a little worried by Rin's plan to move to Australia to study abroad.
Some time shortly before Gou's eleventh birthday, she briefly meets Haruka Nanase, Makoto Tachibana, and Nagisa Hazuki while delivering to Rin the cookie tin he plans to bury the medley trophy in. Neither Makoto and Nagisa nor herself seem to remember the meeting when they later reunite, but Haruka remembers her identity and name later on and Gou herself remembers Haruka, presumably because he's the one that Rin constantly talks about when at home.
While watching her brother compete in the relay, she watches him smile and laugh while they celebrate victory, and this memory burns in her mind after he leaves to Australia. Although he returns every Winter for New Years, she worries over the way he no longer smiles and becomes more withdrawn each year.
Eventually, when Rin returns to Iwatobi only to attend a boarding school and refuses to answer her texts, much less visit home, Gou becomes worried enough about Rin to decide to take action to 'make him smile again'.
PlotHaruka's and Rin's unsuccessful duel, a scarlet-haired girl observes the group with a friend and remarks of them being old acquaintances before Makoto and Nagisa are reprimanded by a teacher for trespassing at the swimming club. As Makoto and Nagisa visit Haruka that evening, they discover the scarlet-haired girl turns out to be Rin's sister, Gou Matsuoka, attempting to pay Haruka a visit. They then learn from her that Rin is now attending Samezuka Academy upon his return from Australia.
After the match, Haruka and the others are once again reprimanded for trespassing on Samezuka Academy grounds. Makoto and Nagisa run into Gou and they all agree that Rin's attitude had dramatically changed in the past few years, simultaneously learning that Gou had been the one who sent him to the Iwatobi Swimming Club while Nagisa suggests that they form a school swimming club.Rei to join the swim club, Gou informs the club that she had successfully scheduled a joint swimming practice with the Samezuka team at their indoor pool, but they would still require a fourth swimmer.
The Swim Club (with their fourth member, Rei) officially starts training in the refurbished pool using an old training regiment of Gou's had unearthed. The following day, the guys try to come up with designs for a club uniform but Gou instead gives Rei's lessons higher priority and makes a revamped swimming regiment during which he must master swimming in one week before their first prefectural tournament. During the weekend, Rei attributes his inability to not having proper gear, hence prompting a visit by the team to a sports store to buy swimming essentials. Gou runs into Seijuro there who was surprised to see her. Later, she overhears Rin's and Haruka's conversation outside the store, getting even more worried over her brother's drastic personality change.
The next morning, the group (who was on the other island during the night) swims back to the coast where their tens are, as well as Gou and Miho, who didn't know what happened last night. When they finally arrive at the coast, Gou and Miho watch them as they sleep and wonder what they're doing. Gou tries to wake them up, but doesn't succeed.
The group attends a summer festival, running into Gou and Chigusa. Makoto compliments Chigusa and Gou for their looks, but Chigusa misunderstood him, thinking that he complimented their yukatas instead of their looks, making Makoto feel a bit uneasy.
After the team finished on one of their practices, Nagisa, Makoto, Rei and Haruka together with Gou, Goro and Miho had a hot pot in Goro's house even though it's summer. There, Gou discovered the old clubs photos, which of course includes Rin in it.
- 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 and Gou have a good, friendly relationship. 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
- Main article: Chigusa Hanamura
Chigusa is a friend of Gou and they at times hang out together.
- 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 great relationship. They act quite friendly towards each other and often do things together. 
- Main article: Rin Matsuoka
Gou is often worried about her brother. One of her main goals 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. In the drama CD Rin and Nitori stalked her because Rin thought she dated a boy every weekend. And they found that actually Gou went with Hanamura to buty a Christmast present for Rin.
- 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. His attempts to go on a date with her are often thwarted by Rin. He usually calls her 'Gou-kun', much to her dismay.
- Main article: Goro Sasabe
Creation and ConceptionHiroko Utsumi, the director of the Free! anime, revealed that both Gou and Miho are really supported by the male staff members. "Her expression is similar to Rin’s. Her eye angle is also similar." she said. "Her hair isn't exactly the same color as Rin’s, but they resemble each other’s. Matching siblings are cute, wouldn't you agree? You sense that she really became emotionally attached to her older brother. I didn't want to have her feel like a character who relied on anyone else, so I made her the kind of girl who’s got her own independent will. She’s a kind of girl who does whatever she wishes. She has her own reasons for joining the swimming club. It’s not that she’s weak as a character; she joined because she would enjoy looking at muscles. Thus we also depicted her discovering her own reason to enjoy the swimming club. Her personality is feminine yet clearly cheerful. I requested to Nishiya-san that I wanted her hair to be long. I think she’s a character who splendidly stands out amongst the cast.".
It is also revealed that Gou is really poor athletically. If she and her brother were both athletic and swam, the animators would have to insert differences between them to show weaknesses. She’s also poor at running. So, Gou only joined the swimming club to watch guys swim. The reason why Gou gets into arguments with Nagisa is because he won't change how he calls her. “Don't call me Gou, call me Kou.” They're the same age, so there’s no hesitance for her to speak like that. Gou has some aspects of her that are childish, so the two of them together feel like a couple of kids arguing with each other. At any rate, Gou is in an important position as a character. She’s Rin’s sister, so she acts as a bridge between him and the Iwatobi swimmers. The director also contributed things she clearly wanted in Gou's personality, like how she loves looking at muscles, so it was immediately put in.
- Gou was named after the Sengoku warlord, Nagamasa Azai's third daughter.
- In contrast to the male characters' feminine names, Gou has a masculine name.
- Both Gou and Nagisa's rooms were exactly copied from North American furniture catalogs and blogs.