Koutarou Matsudaira serves as the catcher and captain of the Meisei High School baseball team during the events covered in Touch 3: Don't Pass Me By. He initially enters the story as the closest friend and battery partner of Kazuya Uesugi, the team's ace pitcher, and he shares Kazuya's dream of reaching the Koshien national tournament. Even early on, he proves to be a dedicated and hardworking player who takes baseball seriously, which shapes his initial resentment toward Tatsuya Uesugi. Koutarou contrasts Tatsuya's perceived laziness with Kazuya's discipline and talent, leading to open clashes and a strained relationship. After Kazuya's death, that dynamic shifts dramatically. Koutarou steps forward as a key leader, eventually becoming the team captain after the seniors graduate, and he must learn to trust Tatsuya as the new ace. The two gradually build a reliable battery, with Koutarou's steady game-calling and receiving providing a crucial foundation for Tatsuya's growth on the mound. His personality is earnest, proud, and sometimes blunt, but his loyalty to the team and his deep desire to honor his late friend's ambitions keep him focused. As the story progresses, he matures from a hotheaded teammate skeptical of Tatsuya into a respected captain who believes in their shared goal, demonstrating a quiet resilience and an unwavering commitment to Meisei's baseball club.