Tomoya Yamaguchi

Yamaguchi receives no substantial characterization outside the game in which he appears. His role is primarily that of a middle-school prospect temporarily placed into an older lineup.

Yamaguchi plays third base and bats third in the reconstructed varsity order. Batting near the top of the lineup indicates that Daimon considers him useful enough offensively to place him ahead of much of the team.

No signature hitting technique or specialized defensive ability is established for him.

Yamaguchi participates in the second game between Seishuu's varsity and prefab squads. With several members of the original varsity unavailable, Daimon fills gaps using middle-school players.

Yamaguchi replaces Kubo at third base while Kazuaki Sakurada takes center field and Koji Mori plays first. The rebuilt varsity loses 2–0, and the defeat ends Daimon's control over Seishuu's baseball program.

Shuugo Daimon places Yamaguchi in the reconstructed varsity for the decisive rematch.

Yuuji Kubo is the original varsity third baseman whose position Yamaguchi fills.

Kazuaki Sakurada and Koji Mori are fellow middle-school players brought into the same lineup.