Jun Yamano is an eight-year-old boy from Machida, southwest of Tokyo. His kind parents—a businessman father and housewife mother—took a holiday trip to Shinjuku only to be separated during a Youja Empire attack. Rescued by the Samurai Troopers and Nasuti, Jun remained under their protection. The warriors and Nasuti became his surrogate family, offering emotional support while his parents were missing. Despite his ongoing worry, Jun forged a strong bond with the group, especially Byakuen, the large white tiger who aided him in Shinjuku. He often kept Byakuen company, gripping the tiger's tail as he skateboarded, considering it both a hobby and transportation.

Jun's innocence and uncorruptible thoughts proved significant. His pure heart enabled him to discover, handle, and effectively utilize the Inochi no Magatama (Jewel of Life), a sacred object crucial against the Youja Empire. This purity, shared with Nasuti, granted them immunity to Youja World corruption because neither harbored greedy or evil inclinations. Their moral clarity allowed them to locate and empower the Jewel, directly aiding the Troopers. In a critical moment, Jun deliberately exaggerated injuries from a battle strike to provoke Shu Rei Fuan's emotional response, successfully breaking Shu's mental block and restoring his armor-summoning ability.

Throughout his time with the Samurai Troopers, Jun showed resilience despite his youth. He admired the warriors as older brothers and adopted the self-styled title "Reppu no Jun" (Jun of the Strong/Violent Wind) to match their elemental conventions. He embraced skateboarding, kendo, and his unconventional companionship with Byakuen, often noted as "riding tigers." Conversely, he disliked studying, carrots, and the threatening Youja forces. While his parents' ultimate fate remained unknown within the narrative, Jun evolved from a vulnerable child separated from his family into an active participant whose emotional and moral strengths repeatedly influenced key victories.