Gakuto Mukahi is a third-year student at Tokyo's prestigious Ice帝都学园 (Hyotei Academy) and a regular member of its storied tennis club. Born on September 12th, he stands at 158 centimeters tall and weighs 48 kilograms, a compact frame that is essential to his unique playing style. He is easily recognized by his distinctive bright red hair, cut into a classic bob or "妹妹头" style. Despite his somewhat delicate or boyish features, his personality is direct, stubborn, and passionate, often belying his initial appearance. He comes from a family consisting of his parents, an older sister, and a younger brother, with his father running an electronics store. However, his relationship with his father is notably poor, leading Mukahi to run away from home and seek refuge at the house of his doubles partner, Yushi Oshitari, as many as seven times a month.

Mukahi's personality is defined by a focus on the present moment. He is a "即将主义者" who pours all of his energy into the immediate present rather than saving strength for the future. This mindset makes him a naturally impulsive and straightforward individual who prefers clear, concrete answers over abstract ideas. This trait is reflected in his favorite school subjects, chemistry and English, where answers tend to be definitive. He has a strong distaste for things that are unclear or frightening, including ghost stories and frogs. In social situations, he is known to be talkative, sending a large number of messages to friends daily, and he cherishes his freedom above all else, strongly resisting any form of control. His enthusiasm for jumping and aerial maneuvers is a near-obsession that forms the core of his identity.

His primary motivation is to utilize his extraordinary leaping ability to dominate the net, a passion that drives his entire approach to tennis. Mukahi's role in the story is as a specialist in "acrobatic tennis" for Hyotei, a team known for its deep roster of talented players. While he often appears as a rival to Eiji Kikumaru of Seigaku due to their similar high-flying styles, his role is firmly established as a member of Hyotei's regular doubles team. He lives by a self-created motto from his elementary school days, "一日一跳" or "one jump a day," which perfectly encapsulates his life philosophy and his approach to the sport.

His key relationships are central to his character. His most significant partnership is with the cool and calculating "genius," Yushi Oshitari. The two first met when Oshitari was sitting on the rooftop water tower, a place Mukahi often visited. Despite their contrasting personalities, Mukahi's fiery and impulsive nature is well-balanced by Oshitari's calm and strategic mind, making them a formidable doubles pair. Beyond the court, they share a deep friendship; Oshitari's family is aware of Mukahi's habit of running away from home, and he is one of the few people who truly understands the acrobat. Mukahi is also childhood friends with teammates Ryo Shishido and Jiro Akutagawa, having known them since elementary school. He and Akutagawa are even next-door neighbors. He maintains a playful and somewhat competitive relationship with fellow regular Wakashi Hiyoshi.

Character development for Mukahi often revolves around the limitations of his chosen style. He possesses incredible flexibility and a vertical leap of 120 centimeters, allowing him to perform his signature move, the "月面翻身截击" or Moonsault, where he hits the ball while momentarily upside-down in mid-air. His acrobatic prowess is considered superior to that of his rival, Kikumaru. However, this explosive and high-energy playstyle comes with a significant flaw: low stamina. He tires much more quickly than other players, a weakness that has been exploited in key matches. In the national tournament, his coach, Sakaki Taro, attempted to mitigate this by pairing him with Hiyoshi for a short, decisive battle, but the strategy ultimately failed when opponents like Sadaharu Inui and Kaoru Kaido deliberately dragged the match into a long endurance contest. Later, during the U-17 training camp, this weakness was ruthlessly exposed by Oshitari in a tie-break match, leading to a crushing 0-7 defeat. This loss forced Mukahi to confront his limitations directly. Through subsequent intense training, he was able to develop a new technique, the Low-Altitude Moon Sault, a more energy-efficient variation of his signature move that allows him to stay in the game longer.

Gakuto Mukahi’s notable abilities are almost entirely focused on his aerial game. As a left-handed serve-and-volley specialist, his playing style is built around rushing the net and using his phenomenal jumping power to hit difficult and unexpected shots. Beyond the Moonsault, his athleticism is further demonstrated by his hobbies, which include bungee jumping, street dancing, and skateboarding. He is deeply committed to his craft, even expressing a childhood desire to grow wings on his back to jump even higher. His entire identity as a tennis player is a blend of artistic flair and competitive spirit, a "华丽飞舞于空中的特技高手" who lives by the jump and, occasionally, falls by it.