Jun Yamano, an eight-year-old boy from Machida, southwest of Tokyo, becomes tragically separated from his kind parents during a Youja attack in Shinjuku on a family trip; his parents vanish and are never seen again. In the aftermath, Jun forms a deep bond with the Samurai Troopers, idolizing them as older brothers and adopting the self-styled title "Reppu no Jun" (Jun of the Strong/Violent Wind) to align himself with their heroic identities.

Possessing a pure and innocent heart, Jun proves uniquely capable of handling and activating the sacred Inochi no Magatama (Jewel of Life), one of three objects able to counter the Nether Realm's power. This purity, and his lack of greed or evil thoughts, also grants him immunity to corruption by the Youja World, a trait shared with Nasuti. Despite his youth, Jun displays remarkable bravery, often standing firm against formidable enemies. He demonstrates psychological insight by strategically feigning injury to provoke Shu Rei Fang into reclaiming his armor's lost power.

His hobbies include skateboarding, often combined with "tiger riding" – grabbing the tail of the giant white tiger Byakuen to be pulled along. He dislikes studying and carrots. Looking up to the Samurai Troopers, Jun gradually matures under their influence, becoming a skilled kendo practitioner who wins a championship tournament by age eleven or twelve.

Jun serves as a crucial moral compass and catalyst for the Troopers. Beyond wielding the Jewel of Life, his unwavering spirit and willingness to face danger without armor or supernatural abilities frequently aid the group. He firmly views himself as part of their team, developing familial bonds, particularly with Touma Hashiba, who treats him like a younger brother despite occasional annoyance at his exuberance. Jun's character arc traces his evolution from a lost child to a determined youth training in martial arts.