Koji Kabuto, the protagonist of Mazinger Z: Infinity, is depicted ten years after the events of the original series. Having once piloted the super robot Mazinger Z to defeat Dr. Hell and the Underground Empire, he has since followed in the footsteps of his father and grandfather by becoming a leading scientist at the Photon Power Laboratory. This shift reflects his maturation from a hot‑blooded and impulsive teenager into a responsible adult who channels his energy into research and development. Despite this newfound discipline, he retains his core bravery and an unyielding will to protect others, which ultimately draws him back into combat when a new threat emerges from beneath Mount Fuji.

His personality balances a lingering recklessness with a deeper sense of duty. He is decisive and courageous in battle, often relying on his instincts and raw determination, but he has also learned to value collaboration with his allies. His relationship with Sayaka Yumi has deepened over the decade; they are now a couple, though his single‑minded focus on work sometimes strains their time together. This dynamic is part of his broader growth, as the film intentionally gives him a character arc centered on reconnecting with the people he fights for.

In terms of abilities, Kabuto remains a highly skilled pilot, renowned for his intuitive control of Mazinger Z and his habit of shouting weapon names like “Rocket Punch!” and “Breast Fire” during combat. Beyond piloting, he demonstrates significant scientific acumen, managing advanced photonic power research and contributing to the development of new technology. His most defining trait, however, is his indomitable spirit, which enables him to persevere through overwhelming odds and inspires those around him to stand with him.