Yamaguchi is a reserved individual who depends heavily on others. Despite being generally friendly, he often laughs along with Tsukishima when he mocks others. He demonstrates dedication through his self-initiated extra training and persistent practice beyond the team's boundaries, revealing his weaknesses in comparison to his teammates.
After a fatal loss in the match against Aobajōsai High, he gained a lot of confidence thanks to his teammates and Makoto Shimada. During the summer training camp, he even stood up against Kei Tsukishima, who was surprised and called him "cool" for the first time.
After a fatal loss in the match against Aobajōsai High, he gained a lot of confidence thanks to his teammates and Makoto Shimada. During the summer tr