Shōsuke Yamada is the younger brother of Gota Yamada, who remains a close friend of protagonist Takeshi Yamato. Residing in Japan, Shōsuke integrates into Takeshi's social circle and frequently appears alongside Takeshi's younger sister Jun Yamada. During early events, Shōsuke endures physical assault by unidentified aggressors, leaving him visibly vulnerable. Takeshi later encounters Shōsuke near a riverbank, where Shōsuke and Jun both show distress. Takeshi intervenes with moral support, delivering an encouraging talk to bolster Shōsuke's resilience. When Takeshi returns to Japan after intensive training abroad, Shōsuke appears at the airport welcoming group alongside Jun and his brother Gota, maintaining his connection to Takeshi's family and friends.