Kōji Kabuto is a teenager who lives with his younger brother Shiro and his grandfather, the brilliant scientist Juzo Kabuto. His parents died in a laboratory accident when he was young, leaving his grandfather as his sole guardian. Kōji is an average high school student whose main pastime is riding motorcycles, at which he is highly skilled. He also possesses considerable talent in martial arts, a skill he often relies on when facing the human-sized agents of Dr. Hell.

His personality is defined by a hot-blooded, impulsive, and reckless nature. He is brash, overconfident, and prone to acting without thinking, which frequently leads him into trouble both in battle and in his personal interactions. He often clashes verbally with Sayaka Yumi, the daughter of Professor Yumi, and their relationship is marked by constant bickering and mutual stubbornness, though a clear undercurrent of affection eventually develops. Despite his rough exterior, Kōji has a strong sense of justice and deep loyalty to those he cares about.

Kōji’s primary motivation is revenge. His grandfather, Juzo Kabuto, is murdered by Dr. Hell’s lieutenant Baron Ashura in the opening events of the story. Before dying, Juzo entrusts Kōji with the task of piloting the giant robot Mazinger Z to stop Dr. Hell’s plans for world domination. This personal loss transforms a carefree youth into a determined fighter. Over time, that initial thirst for vengeance matures into a genuine sense of duty to protect humanity from the Mechanical Beasts and the other monstrous creations of Dr. Hell.

Kōji is the central protagonist and the sole pilot of Mazinger Z throughout the conflict. He operates the robot from the Hover Pilder, a small VTOL craft that docks with the head of Mazinger Z. His role is that of humanity’s frontline defender, facing ever more powerful Mechanical Beasts and devious traps devised by Dr. Hell and his lieutenants. He often fights alongside Sayaka in her robot Aphrodite A, as well as with a group of local motorcycle-riding allies led by Boss.

Key relationships include his bond with his younger brother Shiro, whom he protects fiercely and who sometimes inspires new combat tactics. He regards Professor Yumi, his grandfather’s former colleague, as a mentor and surrogate father figure. His rivalry-turned-friendship with Boss provides occasional comic relief, but Boss and his gang also prove themselves as brave allies in critical moments. With Sayaka, the dynamic is tense yet cooperative, and their partnership becomes essential to the defense effort.

Kōji undergoes significant development throughout the ordeal. He begins as an unskilled and undisciplined pilot who can barely control Mazinger Z, frequently making mistakes that nearly cost him the battle. As he accumulates experience and faces increasingly dire threats, he grows into a capable and courageous warrior. His unyielding will becomes his greatest asset, allowing him to overcome situations where even the supposedly indestructible Super Alloy Z proves insufficient. He learns to channel his recklessness into focused determination, and by the final confrontation with Dr. Hell, he has matured into a true hero.

Notable abilities include his mastery of motorcycle riding and his physical combat skills, which enable him to handle small-scale threats without the robot. His most famous trait is his habit of shouting the names of Mazinger Z’s weapons as he activates them, such as Rocket Punch and Breast Fire, a practice that becomes iconic for the entire super robot genre. As a pilot, he develops excellent reflexes and tactical instincts, allowing him to use Mazinger Z’s diverse arsenal—including eye beams, rocket fists, elbow missiles, and the rust hurricane—to full effect even when the robot itself is damaged or outmatched. His sheer resilience and refusal to surrender often prove more decisive than any piece of technology.