Koshi Sugawara is a third-year student at Karasuno High School where he serves as the vice-captain of the boys' volleyball team. He was the team's starting setter before the arrival of the prodigious first-year Tobio Kageyama. Following this shift, Sugawara became a substitute setter and pinch server, gracefully accepting a role that involved less playing time but remaining deeply committed to the team's overall success. Sugawara is characterized by a calm, gentle, and deeply supportive personality. He acts as a pillar of emotional support for his teammates, often soothing tensions and encouraging a positive team atmosphere. He is highly perceptive and intelligent, capable of reading the flow of a game and understanding the needs of those around him. Despite his gentle demeanor, he also displays a playful and mischievous side, particularly with his close friends. His primary motivation stems from a genuine love for volleyball and a firm desire to avoid future regrets, which drove him to continue playing for the team even as a third-year when many of his peers chose to retire from club activities. Within the Karasuno team, Sugawara functions as a vital emotional anchor and tactical mind. He shares a strong partnership with captain Daichi Sawamura, complementing his leadership. His most significant relationship is with Tobio Kageyama. Rather than resenting the first-year for taking his starting position, Sugawara identifies Kageyama's weaknesses as a leader and actively helps him understand and connect with his teammates, guiding him toward a more collaborative style of play. Sugawara is also instrumental in fostering team cohesion, interacting warmly with players like Asahi Azumane, Ryunosuke Tanaka, and Yu Nishinoya. His perceptiveness allowed him to devise crucial strategies, such as the communication cues for Kageyama and Hinata's quick attack. Sugawara's character arc is defined by the transition from a starting player to a supportive role. His greatest development is his acceptance of this reduced competitive visibility while maintaining his dignity and finding fulfillment in contributing to the team's collective success, proving that influence extends beyond being on the court. As a player, he boasts high marks in volleyball intellect and technique. He relies on strategic play and a deep understanding of the game rather than raw physical power. He is a reliable pinch server capable of turning the momentum of a set and is exceptionally skilled at calming the team and making critical tactical observations during high-pressure moments, such as the Dumpster Battle against Nekoma.