Retsu is a human born on Earth who had originally traveled with Chiyo, Timpani, Arcti, and Matoma. Although originally proving his worth towards the team, his human strength could not compete with the other fighters, and retired from fighting after the Universal Tournament.
"I don't care that I'm just a human, I will never stop trying to get stronger, and once I do, you'll pay!" - Retsu
Stubborn and insistent on becoming stronger, Retsu tries his whole life trying to become stronger than the other members of his team. His goals are fueled by jealousy, believing his weakness is his humanity. Despite this, he has longing determination and only quits his role as a Z-Fighter after the Universal Tournament.
Retsu started his days under the training of an old sage, who taught him after the death of his father. Although he had initial spite for the sage, as he had disciplined him and thrust him into harsh training, he eventually learned to appreciate him and return to his training
Joining the Z-Fighters
After making his way into a city, Retsu is caught in the middle of an alien attack by the saiyan Matoma and the namekian Timpani. Here, he encounters the son of Makoto, Chiyo, and the two attempt to subdue Matoma and Timpani to no avail. After getting beat in battle, the two encounter the son of Ridge, Arcti, and decide to form an alliance to defeat the alien invaders.
The three encounter the aliens once more, and during the battle Retsu is forced to kill Chiyo while he holds down Matoma. Realizing his defeat, Timpani decides to stay on Earth and instead live and fight in peace there. After the gruesome battle, the three go on a quest to find the dragon balls and wish their friends to life.
The Return of Cauce
After collecting the dragon balls, they had wished Matoma and Chiyo back to life. Matoma has a tough time readjusting to the Earth, yet Chiyo had managed to train during his time in the afterlife, and returned with the strength of Kaio-Ken.
After sparring with Chiyo and seeing his newfound power, Retsu decides to continue his training to make up for the lost time he had spent searching for dragon balls. While this happens, a villain re-emerges from Ocari's Lookout, Cauce. Cauce scours the Earth for a body to possess and settles on Chiyo. Once he implants himself in Chiyo, he wreaks havoc throughout the planet. The Z-Fighters get together in an attempt to stop Chiyo. During their valiant attempt to stop him, Retsu is mortally wounded, and dies on the battlefield.
Return to Earth
After a year in the afterlife, Retsu returns to Earth having learned the technique "Atomic Punch", a move that creates explosions from the punches he delivers, while simultaneously hurting himself. Once he returns, he notices that Chiyo had left the team to temporarily train with his father in the mountains.
Shortly after he is wished back to life, however, a Saiyan named Callion who was previously friends with Matoma has sought him out to get revenge for Matoma's betrayal. The foe transforms into a Super Saiyan and is not affected by any of the blows dealt by the rest of the team. Having to flee, the team settles on a nearby island where they begin to argue.
Retsu decides to test his new techniques on Arcti after the argument escalates into a battle. Seriously damaging his arms during the battle, he only manages to land several successful hits on Arcti before having to flee. After the skirmish, the gang re-encounters Chiyo, who shows off his Super Saiyan transformation as a result of his training. Using this and the power from the other members of the group, the warriors attack Callion once more. During the battle, Matoma had managed to also receive the Super Saiyan transformation, and Retsu had managed to achieve a form known as "Super Human".
After many years of peace in the world, the members of the Z-Fighters had achieved many incredibly powerful forms and were recruited by the God of Destruction to fight against Universe 13. Retsu was not included in the lineup due to a limit of 8 people and spent the tournament on the sidelines.
During the last battle however, a villain named Yin Yang appeared, leading an assortment of other villains from both universes. Yin Yang fuses his energies with Kanji and becomes The End. Retsu is then sent to another universe, where a villain named Black Resurken roams and wreaks destruction. After managing to escape that universe and return to the tournament stage, the warriors attack Yin Yang.
As a final resort, every warrior including Retsu gives their energy to Ryuken in an effort to defeat Yin Yang, and succeeds in doing so. Afterwards, Retsu decides to give up fighting, and stay on Earth for good.
Retsu now lives on Earth as a mere farmer, and has settled down with a wife and children. He was asked to be a fighter in the Universal Survival Tournament, but declined in fear that he would not be strong enough.