Rei is the successor of Nanto Suichō Ken ("South Dipper Waterfowl Fist") style and is one of the Nanto Rokusei Ken, bearing the destiny of the "Star of Justice".

When the Man with Seven Scars (Jagi) killed his parents and kidnapped his sister Airi, Rei abandoned his humanity and roamed the wastelands as a lone wolf. Rei was hired by the Fan Clan to infiltrate Mamiya's village as one of its bodyguard. However, Rei betrayed them and helped Kenshiro thwart them off, believing that siding with the villagers with Ken on their side would be more beneficial than working with the Fangs. Afterward, Rei went to the hideout of the Fangs with Ken and Mamiya to defeat their leader. However, the Fangs have managed to capture Airi from her previous captors and used her as leverage to coerce Rei into fighting Ken for them. However, Rei and Ken managed to trick the Fang Clan into releasing by striking each other's vital points at the same time, placing both of them in a temporary false state of death. After the Fang Clan was defeated, Rei was reunited with Airi.

Afterward, Rei would become one of Kenshiro's most trusted allies. He exposed Amiba's true identity at the Village of Miracles and then accompanied Kenshiro to the city of Cassandra, where the real Toki was being held at. Although Toki was saved, he was forced to rush back to Mamiya's village when he learned that Ken-oh's army began to mobilize his troops. Rei fought the leader of the invasion squad and then challenged Ken-oh himself to a fight. However, Rei was defeated by Ken-oh, who struck the vital point Shinketsushū on Rei, sentencing him to three excruciating days to live.

Later, after rescuing Mamiya from Medicine City, Rei learned that she was once one of Yuda's captives before she escaped and became the leader of her village. Swearing to avenge Mamiya's honor, Rei dedicated the last days of his life in tracking down Yuda and challenging him to a duel. However, Yuda managed to elude him, and Rei almost died without his final battle. However, Toki extended Rei's lifespan for another day, striking the vital point Shinreidai, which had the side effect of turning his hair white as well. Afterwards, Rei entered the final showdown with Yuda, and after a long and hard match he defeated Yuda with the Hishō Hakurei, the Soaring White Splendor. After the battle, Rei tells Kenshiro to live on as the light of the new world and then spends the final night of his life in a one-man hut, which was later burned with his remains still inside.