Kominato Haruichi is a student at Seidou High School and the younger brother of Kominato Ryousuke, originating from Kanagawa Prefecture. He joins the baseball team as a first-year and plays as a second baseman, later becoming part of the keystone duo. His personality is calm and quiet, often acting as the sober counterpart to Sawamura Eijun's energetic behavior, and he has a habit of speaking bluntly, which can inadvertently spark rivalry between Sawamura and Furuya Satoru when he praises them. Despite his reserved demeanor, he is highly ambitious and driven to secure his brother's position on the first string, working diligently to improve his stamina, which is his main physical shortcoming. His relationship with Ryousuke is complex, marked by admiration and a desire to surpass him, while his bonds with teammates like Sawamura and Furuya are close and supportive. Haruichi possesses natural baseball talent, highlighted by his pinpoint batting accuracy that allows him to control the ball's placement and his sharp defensive abilities, including quick reflexes and the capacity to make plays while in motion. His keen baseball sense enables him to make split-second decisions during games, and he continuously develops by gaining confidence and establishing his own identity on the team.