Rei, the Phoenix, ranks among the Four Saint Beasts. His debut unfolds during a critical confrontation between Gorō Mutsumi and Tsubasa, where he interrogates Gorō about their bond. Rei hypnotizes Gorō into boarding a ferris wheel, triggering a mechanical failure that nearly kills him until Tsubasa overcomes her acrophobia to intervene. Rei then vanishes.

His antagonism escalates as he conspires with fellow Saint Beasts Goh, Shin, and Gai to ensnare Gorō. They lure him into dangerous work at an abandoned factory, aiming to inflict harm. This vendetta originates from Gorō’s past incarnation as the sage Seijya, who sealed the divine powers of the Four Saint Beasts centuries prior and stole their sacred artifacts—Rei’s Wings of the Red Phoenix.

Rei sports waist-length purple hair and orange eyes. His signature attire combines a turtleneck, coat, and qipao-inspired garment, often paired with a headdress. He maintains fraternal ties to the other Saint Beasts, specifically as the younger brother of Goh, the Azure Dragon.

Though Rei’s personal history remains unexplored, his actions consistently mirror the collective agenda of the Four Saint Beasts: thwarting Gorō’s destiny to forge harmony between humans and animals, retaliating for their sealing and the theft of their relics.