Naoto Kaguyama (加具山直人 Kaguyama Naoto) is a second year student and Musashino Dai Ichi's former starting pitcher.
Background
Generally, Kaguyama is the pitcher for the first three-four innings before Haruna takes over, with Kaguyama being the right fielder for the rest of the game. This works out well for both of them as Kaguyama is not a strong pitcher, and Haruna doesn't want to exceed his 80 pitch limit.
Shown in a flashback, Kaguyama had been planning to quit because Haruna was clearly more talented than him, however Haruna's hardworking attitude convinced him to stay on the team because he loves playing baseball.
Starting from the ARC match, Haruna decides to pitch for the whole match, which Kaguyama supports for the sake of the team.