Gakuto Zaitsu is a fourth-year student at Doushisha University and captain of its rugby team. He plays as a hooker in the forward position, wearing the number 2 jersey, and serves as the central figure guiding the team.

Physically, Gakuto possesses a muscular build with distinctive neck-length purple hair styled with long bangs swept to the right. His red eyes and visible chin stubble create an imposing first impression. Despite this stern exterior and a reserved demeanor that gives teammates a "scary vibe," his underlying personality is considerate and reliable. His natural leadership is acknowledged within the team, particularly by Ikuto Yufu.

His character is demonstrated when Natsusa Yuzuki returns post a motorcycle accident that ended his playing career. While others crowd around Natsusa, Gakuto refocuses the team on practical matters, instructing them to stretch. He privately checks Natsusa's commitment to becoming manager, emphasizing respect for his wishes. When Natsusa voices anxiety about being annoying, Gakuto becomes visibly flustered, revealing discomfort with emotional displays. An initial instinct to pat Natsusa's head shifts to a shoulder pat upon remembering the injuries, showcasing his attentiveness and restraint.

Gakuto's leadership blends assertiveness with empathy. Ikuto Yufu initially misinterpreted his commanding presence as haughtiness but later recognized it as dedication to the team's success, highlighting Gakuto's capacity to inspire through high expectations coupled with genuine support.

The etymology of his name reflects character aspects: "Gakuto" combines "mountain, peak, point" (岳) and "ten" (十), while "Zaitsu" derives from "fortune, riches" (財) and "haven, port" (津).