Shintarou Nishihiro is a first-year student in Class 3 at Nishiura High School. He shares a close bond with his family—grandparents, parents, and a younger sister—often playing with her at home. Academically gifted, he ranks among the smartest first-years, achieving high test scores without extensive studying. He stands 170 cm tall, weighs 60 kg, has blood type O, and was born on February 10.

With no prior baseball experience, Nishihiro joined the Nishiura baseball team as a beginner. His interest sparked during middle school after reading a baseball manga, planting a desire to try the sport despite initial hesitation about starting late. Encouraged by classmate Oki Kazutoshi, he joined the club and developed a deep affection for baseball. He wears uniform number 10 and primarily serves as a reserve outfielder. His limited experience keeps him off the regular starting lineup, frequently placing him on the bench during games.

During official matches, Nishihiro acts as the third base coach when the team bats, offering strategic guidance to runners. Defensively positioned in left field, his outfield performance steadily improves through intensive training. While his skills show noticeable development, he isn't yet a full substitute for the primary outfielders, contributing to his frequent status as a substitute. Despite irregular playing time, he remains highly motivated, actively supporting teammates from the bench and maintaining a positive attitude about his supportive role.