Kyōtarō Suga is a first-year student at Kiyosumi High School. He is a childhood friend and current classmate of Saki Miyanaga, and during middle school he was a member of the handball team, reaching the prefectural final in that sport. He is the only male member of the Kiyosumi High School mahjong club, and it was he who persuaded Saki to join the club in the first place. His own mahjong skills are at a beginner level, and as a result he does not participate in official tournament matches for the team. Instead, he takes on a supporting role within the club, handling tasks such as running errands, preparing food, and doing heavy lifting. He also occasionally helps the team by making tacos for fellow club member Yuuki Kataoka, who relies on the food to maintain her concentration during play.

In personality, Kyōtarō is generally easygoing, friendly, and approachable. Despite sporting blonde hair that might suggest a delinquent appearance, he is mild-mannered and integrates naturally into the club’s mostly female environment. He is willing to take on whatever chores are assigned by club president Hisa Takei and accepts the teasing or rough treatment he sometimes receives from Yuuki with good humor. He is also perceptive enough to understand the emotional states of his friends, such as when he explains to Saki that Nodoka Haramura’s feelings are complicated after a tense match between them. He harbors an unreciprocated crush on Nodoka, and later shows a brief interest in Mihoko Fukuji as well.

His primary motivation is to support Saki and the rest of the Kiyosumi team in their quest to reach and compete in the national inter-high school mahjong championship. He takes pride in being the person who first brought Saki into the world of tournament mahjong, even if he himself is not skilled enough to play. During the events of Saki - The Nationals, he continues in his behind-the-scenes role, accompanying the team to Tokyo and providing logistical and moral support. He does not undergo any significant development in terms of his own mahjong ability, nor does he take on a more active competitive role; his function remains that of a loyal assistant and comedic foil within the group.

He is on good terms with all the regular members of the Kiyosumi club. Saki calls him Kyō-chan and treats him with casual familiarity. He interacts frequently with Yuuki, who both teases him and relies on his taco-making. Hisa often orders him around without much ceremony, but she also trusts him with important tasks. Outside of the club, he is not shown to have many other close relationships within the story. His role in the narrative is primarily that of an observer and helper, providing comic relief and underscoring the contrast between his own lack of skill and the extraordinary talents of the female players. He has no notable special abilities related to mahjong and his presence is felt most strongly in the club’s daily life and preparation for competition rather than in the matches themselves.