Jun Yamano is an eight-year-old boy from Machida, southwest of Tokyo, with kind parents. He became separated from them during a family trip to Shinjuku when the city faced a Youja invasion, leaving him alone and vulnerable. Discovered amidst the chaos by the Samurai Troopers, they took him under their protection. Nasuti Yagyu and the warriors provided care and emotional support, helping him cope with his loss. He formed a particularly strong bond with the white tiger Byakuen, who aided him during the initial attack, often seen grabbing Byakuen's tail while skateboarding, a hobby he greatly enjoyed.

Intensely admiring the warriors as older brothers, Jun styled himself "Reppu no Jun" (Jun of the Strong/Violent Wind) to emulate their naming conventions and feel part of their group. His innocent and pure-hearted nature proved crucial, enabling him to discover, handle, and activate the Inochi no Magatama (Jewel of Life), one of three sacred objects. His purity allowed him to wield its power without corruption, vital in later battles. This lack of greed or evil thoughts granted him immunity to the Youja World's corrupting influence, a trait shared with Nasuti, allowing both to locate and empower the Jewel when others could not.

Jun demonstrated unexpected bravery, such as when Shu Rei Faun lost faith in his armor. Understanding the gravity, Jun deliberately let himself be struck and pretended severe injury, successfully provoking Shu's protective instincts and reigniting his resolve. Jun disliked studying, carrots, and the Youja forces threatening his friends. His father was a businessman and his mother a housewife, suggesting relative affluence.