Soran Tachibana is the son of Dr. Tachibana, the scientist behind the antiproton bomb who fled Earth with his family to prevent its weaponization. A catastrophic accident during their space journey destroyed their craft, killing Soran's parents. Only Soran and his sister escaped via emergency capsules, becoming separated in the void. Soran's capsule was retrieved by inhabitants of the planet Soran, a world with crushing gravity fifteen times Earth's. To save him and enable survival in this extreme environment, the aliens performed extensive cybernetic augmentation, transforming him into a cyborg. They named him Soran after their world.

Years later, Soran returned to Earth accompanied by his squirrel-like pet, Chappy. His primary mission was finding his lost sister, though he later learned she had not survived. On Earth, his cybernetic body granted him physical capabilities fifteen times greater than a normal human, including immense strength, speed, and resilience. He resided with archaeologist Dr. Kotsuki and his daughter, Mika. While continuing his search, Soran used his extraordinary powers to aid Dr. Kotsuki and Mika, intervening in conflicts and unraveling mysteries. His actions were consistently driven by justice and protecting others.

Soran maintained a distinctive appearance often featuring space-themed attire and was frequently seen with Chappy. His unique history—a human reshaped by alien technology into a cyborg, marked by the loss of his family—fundamentally shaped his motivations and deeds throughout his time on Earth.