Reiji Amemiya is a transfer student joining Yamato Ichidaiji's class. Possessing good looks yet standing apart because of his unconventional personality, he remains largely unpopular. He moves through the corridors like a shadow, elusive and forming few human bonds, instead seeking companionship with cats. This behavior stems from deep emotional trauma inflicted by the Draktor alien invasion, which claimed most of humanity, including his family. Rescued from this devastation by Professor Simon Raider, who adopted him, Reiji spent the next three years within a Shelter Ixia research facility. There, scientists studied and developed his latent psychic power, "Psycho-Rise." Following this intensive period, he integrated into Ixia's general populace.

His path eventually led him to become the pilot of the Megaton-class Rogue, Arthur. Named after the legendary king, the Arthur specializes in close-quarters combat, its centaur-like lower body granting exceptional mobility and agility. Reiji's Psycho-Rise ability, honed within the facility's labs, proves vital for piloting. When activated in battle, it shifts him into a "Sai equalize" state, where he unleashes ferocious force against enemies.

Reiji's appearance features a grey suit with distinctive purple square bottoms and black boots. Beyond the cockpit, he voices introspective thoughts, expressing uncertainty over his ability to protect others and sadness linked to conflict. He maintains a quiet, mysterious air, rarely speaking at length.

In broader media appearances, like Yo-kai Watch crossovers, Reiji is consistently depicted alongside the Arthur mecha, reinforcing this association. He is described as a "man of few words," his mysterious nature sharply contrasting with his combat ferocity. His journey reflects a struggle between his traumatic past, initial pacifist reluctance to fight, and eventual acceptance of his role as a defender against the Draktors.