Gou Matsuoka, Rin Matsuoka's younger sister and an Iwatobi High School student, takes charge as manager of the Iwatobi Swim Club. She plays a crucial role in forming the team by recruiting essential members like Rei Ryugazaki, ensuring they meet the four-swimmer requirement for tournaments. Her support extends beyond recruitment, actively backing the club's activities and training regimens. Energetic and determined, Gou displays a serious fascination with fitness and musculature, often evaluating physical conditioning during events like muscle contests. Her enthusiasm sometimes sparks comedic chaos, such as struggles with childcare tasks like diaper changes, revealing occasional impulsiveness. Despite moments of clumsiness, she demonstrates unwavering dedication as manager, sister, and friend. Her relationship with Rin forms a core part of her background. Having witnessed his relay involvement since childhood, Gou deeply cares for his happiness and well-being. This concern encompasses Rin's friendships, especially during conflicts involving figures like Sousuke Yamazaki, who views Gou as a sister. She navigates sibling dynamics with protectiveness and occasional exasperation, such as enlisting Rin's help for urgent tasks. Gou forms meaningful friendships with the Iwatobi Swim Club members—Haruka Nanase, Makoto Tachibana, Nagisa Hazuki, and Rei. Valued as an equal within the group for her contributions, she transcends being merely "Rin’s sister" or a stereotypical female presence. Her interactions include lighthearted moments, like being the object of Momotarou Mikoshiba’s crush. Extended narratives, such as the "Hanakotoba" story, explore potential romantic connections like one with Makoto. Throughout her development, Gou seeks personal significance beyond supporting others, expressing a desire for moments highlighting her identity as swim club manager and her individual efforts. Discussions about her role in the series acknowledge her growth from a secondary figure to one possessing complex relationships and personal aspirations.