Rei ( レイ ) is the successor of the martial art Nanto Suichōken ( 南斗水鳥拳,"South Star Swan Fist" or "South Star Waterfowl Fist"). Nanto Suichōken is one of the 108 schools of Nanto Seiken ( 南斗聖拳, "Sacred Fist of the South Star"). Rei is a part of the Nanto Roku Seiken ( 南斗六聖拳, "The Six Sacred Fists of the South Star") which represents the six top masters of Nanto Seiken . The six southern styles in the Nanto Roku Seiken represent the six stars of the Nanto Roku Sei (南斗六星, "South Dipper Six Stars") which is a Chinese constellation. Nanto Suichōken represents the Star of Justice ( 義星 , Gi-sei) which symbolizes heroism, and being born under that star, Rei is destined to live and die to protect those in need.
Nanto Suichōken is said to be the most graceful of the Nanto Seiken styles. With a focus on aerial attacks, its primary usage is for close-range attacks. It uses the hands or air pressure to split the body into pieces.
Nanto Ko Ha Ryū (南斗虎破龍, "South Dipper Tiger Destroys Dragon") - Causes its target to fall into a state of false death.
Danko Sōsai Ken (断己相殺拳, "Self-Sacrifice Offset Fist") - Kills an opponent at the expense of the user.
Suzaku Tenshō (朱雀展翔, "Expansive Flight of the Red Sparrow") - Face-cutting technique.
Hien Ryūbu (飛燕流舞, "The Flowing Dance of the Flying Swallow") - The most beautiful technique. An aerial, spinning attack.
Hishō Hakurei (飛翔白麗, "Soaring White Loveliness") - The ultimate Nanto Suichōken technique. A jumping mid-air double stabbing attack.
Rei described his own existence as "living like a starving wolf." Having no provisions of his own, Rei disguised himself as a woman and lured bandits into approaching him in order to take their food. Rei accomplished this by covering himself with a large piece of pink material and taking on the mannerisms of a woman. When the bandits got close enough, Rei revealed himself as a man. After questioning his waylayers to gather information on the whereabouts of the man with seven scars, Rei quickly killed them using his formidable martial arts. Rei was after the man with seven scars and he intended to kill him. The main protagonist of Fist of the North Star, Kenshiro, had seven scars on his chest.
Rei met Kenshiro, Mamiya, Bat and Lyn in a village that was being harassed by a group of bandits called the Fang Clan. Rei was uninterested in anything except exacting his revenge on the man with the seven scars and even allowed the Fang Clan to hire him as a spy. After taking a job as guardian of the village, Rei betrayed the Fang Clan and joined forces with Kenshiro and Mamiya. It was clear that Rei's alliance with anyone would only last as long as it served his goal to find and kill the man that he was after.
It is revealed that Rei left his home village to train in the art of Nanto Suichōken. After becoming the successor of Nanto Suichōken he returned to his village only to find out that it was attacked. With his dying breath, Rei's father told him that his mother was killed and his younger sister, Airi, was kidnapped. The only information that Rei had on the attackers is that they were lead by a man with seven scars on his chest. Rei set out to find and kill the man with seven scars and rescue his sister.
After the Fang Clan killed Mamiya's younger brother, Kou, Rei decided to take on the Fang Clan. Rei felt sorry for Mamiya and the loss of her younger brother. Although it seemed that there was transference of his feelings for his sister unto Mamiya, he also had a great deal of respect for her as a leader and a fighter. Kenshiro and Mamiya decided to go with Rei to fight the Fang Clan given their desire for a common goal, to exact revenge on the Fang Clan and allow Mamiya's village to live in peace.
In retaliation for Rei's betrayal the leader of the Fang Clan acquired Rei's sister, Airi. When Mamiya failed to rescue her, she became a prisoner of Boss Fang and both the women were hostages. To Rei's horror, Airi told him that she had been sold as a slave and had shut her heart to the world and lost her sight. Boss Fang ordered Rei to kill Kenshiro or he'd kill Airi and Mamiya. In order to rescue them, Kenshiro signaled Rei with Seikyokurin ( 聖極輪 , "Holy Perfect Circle ") which told Rei to stage a fight to the death. Rei used the secret technique Nanto Ko Ha Ryū (南斗虎破龍, "South Dipper Tiger Destroys Dragon") and Kenshiro used Hokuto Ryū Geki Ko ( 北斗龍撃虎 , "North Star Dragon Attacking Tiger ") that caused them both to fall into a state of false death. While the Fang Clan were distracted by their sense of victory, Kenshiro and Rei were able to turn the tide, rescue the hostages and destroy the Fang Clan. After Kenshiro helped to rescue Airi and restored her sight using pressure points, Rei decided to help Kenshiro in any way that he could. Kenshiro made Rei feel peaceful and Rei no longer lived like a "starving wolf." Even after Kenshiro reveals that he has seven scars on his chest Rei knew that it wasn't Kenshiro who kidnapped Airi.
The man with the seven scars that attacked Rei's village and kidnapped his sister is found out to be a man named Jagi. Jagi was one of Kenshiro's adoptive brothers who trained in the art of Hokuto Shinken. Kenshiro decided to go after Jagi, who was masquerading as Kenshiro. Jagi was calling himself "Lord Kenshiro" and terrorizing villagers to tarnish Kenshiro's reputation. Jagi was jealous of Kenshiro being named the successor of Hokuto Shinken. Kenshiro killed Jagi and learned that the other two Hokuto Shinken brothers, Toki and Raoh, were also alive. Kenshiro set out to find his brothers and Rei and Mamiya went to help.
Kenshiro eventually links up with Toki, and the group heads out to confront the last and oldest Hokuto Shinken brother, Raoh. Raoh had become a tyrant and called himself Ken-oh ("Fist King"). Kenshiro decided to go after Raoh for imprisoning Toki and terrorizing the people. Rei tried to fight Raoh for Kenshiro. He used the technique Danko Sōsai Ken, but Raoh saw through Rei's attack. Raoh threw his cape at Rei, thereby distracting him. This allowed Raoh to hit the pressure point Shinketsushū ( 新血愁) which gave Rei three days before erupting blood and dying.
Rei learned that Mamiya was once a slave of a man named Yuda. Yuda was the successor of Nanto Kōkaku Ken (南斗紅鶴拳, "South Dipper Crimson Crane Fist" or "Flamingo Fist"). As Rei's last act in life, he decided to kill Yuda for the torment that he caused Mamiya. In order to do that he allowed Toki to prolong his life for an additional day by hitting the pressure point Shinreidai ( 心霊台). The extra day of life came at the cost of great physical pain. It is said that the pain can be enough to drive a person mad, but Rei endured the pain and emerged with his mental faculties intact. However, Rei's hair turned white in the process.
During the climactic fight with Yuda it is revealed the Yuda was always jealous of Rei. During a demonstration in front of Nanto students, Rei performed the technique Hien Ryūbu. The technique is so beautiful that Yuda spent his life chasing its beauty. Yuda attempted to overcome Rei by flooding the battleground with mud and disabling Rei's footwork, the key to Nanto Suichōken's most deadly techniques. Kenshiro lowered the flood level by blocking the flow of water and Rei launched into the air using his hands to propel off the surface of the mud. He defeated Yuda using the technique Hishō Hakurei (飛翔白麗, "Soaring White Loveliness"), Nanto Suichōken's ultimate technique. In his dying moments Yuda admitted that he always respected Rei and that Rei and Nanto Suichōken's is the most beautiful style.
Finally, with his life at an end, Rei isolated himself in a room. He didn't want his friends to see him suffering and hemorrhaging blood. In the last moments of his life Rei displayed his gratitude for Kenshiro bringing peace to a man who had once abandoned his humanity for revenge. He voiced his love for Mamiya and hoped for a better life for her, a life as a woman and not a warrior. He expressed his love for his sister Airi and he basked in his thankfulness for his friends Bat, Lyn, and Toki. Rei died with no regrets. He fulfilled his destiny of being born under the star of justice, living and dying for those he loved.