Retsu Seiba is the older brother of Go Seiba by one year. His signature appearance includes a green hat and red-themed elements covering his hair, eyes, gloves, and shirt, a color scheme extending to his Mini 4WD cars.

Personality-wise, he is patient, level-headed, and analytical, contrasting with Go’s impulsive nature. He exercises strong self-restraint and approaches racing strategically, prioritizing control and stability in car design. Despite his calm demeanor, he occasionally shows annoyance, particularly toward those who anger him. He values fair competition and rejects underhanded tactics. As captain of the TRF Victorys during the World Grand Prix (WGP), he emphasizes teamwork and formation racing, often devising strategies leveraging group coordination over individual speed.

His racing journey began with the Super Astute Jr., followed by the Sonic Saber—a prototype gifted by Dr. Tsuchiya. The Sonic series became his signature line, emphasizing cornering agility and off-road capability. Key models include Vanguard Sonic, Hurricane Sonic, Buster Sonic (used in WGP), Blitzer Sonic, and later iterations like Great BlastSonic and CosmoSonic in the Return Racers sequel. His cars are known for balanced performance, though he temporarily experimented with battle-oriented modifications under Professor Oogami’s influence, a decision he later reversed. He pioneered the "V Formation" technique, synchronizing multiple cars for tactical advantages during races.

After retiring from competitive racing, he became a space development engineer, working on projects including a space probe named after one of his Mini 4WD cars. He maintains ties to the racing world through appearances in events like the Mini 4WD Hyper Dash Grand Prix, where his Sonic cars feature as opponents. His legacy includes inspiring team-oriented racing philosophies and advancements in Mini 4WD technology.