Gou is Rin's younger sister. She is a 1st year student at Iwatobi High School. She has an easygoing and refreshing personality but is always worried about her brother, Rin. She joined the Swim Club as the manager in hopes that she, along with Haruka, Makoto, Nagisa and Rei, can help change Rin back to his old self.

As the Iwatobi High School Swim Club's manager, Gou is quite efficient and supportive one, coming up with training routines for the team, searching for practice partners and finding out the opponent team's information.

She dislikes to be called by her real name Gou and prefers to be called "Kou" (same kanji reading). Though she eventually gives up, mostly due to Nagisa always insistently calls her by her real name.

Gou has a muscle fetish as she tends to blush around men when admiring their muscles.