Tsūgen Sasaki is a second-year Doshisha University student and a member of its rugby team, wearing the number 7 jersey as a right flanker in the forward position. He has short black hair, green eyes, and a medium build. His personality is characterized as spiritual, demonstrated by his commitment to daily good deeds and calm demeanor. He interacts supportively with teammates, notably getting along well with Seiichirō Shingyōji.

During a conversation between Natsusa Yuzuki and Sunao Konoe about bringing Ibuki Ueoka back to the team, Tsūgen was present alongside Pongsaklek Yunu. While Yunu expressed curiosity about their discussion, Tsūgen advised Yunu that understanding their Japanese was unnecessary. In Episode 7, his spiritual nature is further shown when he guides Seiichirō Shingyōji and Pongsaklek Yunu through a meditation session aimed at helping them achieve greater focus, likely for rugby performance or personal balance.

The etymology of his name reflects meanings related to passage or communication (通, "tsuu") and connection or string (弦, "gen"). His surname Sasaki combines "help" or "aid" (佐, "sa") with "tree" or "wood" (木, "ki").