Koutarou Matsudaira anchors the Meisei High School baseball team as its catcher. He shares a close friendship with Kazuya Uesugi, forming a strong on-field partnership where Matsudaira consistently catches for Kazuya. This dynamic establishes Matsudaira as Kazuya's primary battery mate and trusted confidant. He also serves as a supportive presence within the team, contributing to Meisei's efforts during challenging periods, such as coach Eijiro Kashiwaba's rigorous training regimen. Matsudaira's role remains consistent throughout official Touch media, including his involvement in the third movie which focuses on Meisei's baseball activities and team dynamics.