Koichi, a Japanese junior high student codenamed Babel II, uncovers his extraordinary heritage as a descendant of Babel—an alien marooned on Earth millennia ago after his signal tower was destroyed. Inheriting Babel’s legacy, Koichi is chosen by the sentient Tower of Babel as Earth’s defender, clashing with Yomi, a rival heir bent on conquest.

Initially gifted with heightened intellect, physical prowess, and regenerative healing, Koichi’s psychic arsenal grows to encompass telepathy, energy manipulation, telekinesis, and mental dimension traversal. Later iterations grant him levitation, clairvoyance, force fields, pyrokinesis, and energy projection. He crafts physical disguises, though his imperceptible mind betrays him to psychics.

His saga spans multiple timelines. In *His Name Is 101*, the CIA imprisons him as Subject 101, harvesting his DNA to engineer superhumans. Freed but stripped of his guardians—Rodem, Ropross, Poseidon—he hunts these clones worldwide. Decades later in *Babel II: The Returner*, ageless Koichi confronts a resurgent Yomi and U.S. forces, wielding time manipulation and spacetime distortion, stabilized by the Tower’s AI against mental burnout.

Masked as Big Fire in *Giant Robo: The Day the Earth Stood Still*, he commands upgraded guardians—Achilles, Garuda, Neptune—through cryptic agendas hinting at unfathomable power.

Overexertion risks rapid aging or energy depletion, while prolonged combat strains his cognition. Enemies exploit his empathy, luring him with civilian harm—a tactic he strategically reverses. Morally ambiguous, Koichi balances protector duties with ruthless pragmatism, eliminating threats and manipulating outcomes to uphold global equilibrium, blurring heroism and calculated sacrifice.