Koji Kabuto pilots the super robot Mazinger Z. He has an athletic build, black hair combed backward with distinctive sideburns, and is often seen wearing a specialized pilot suit topped by a helmet resembling the Photon Power Laboratory.

His personality blends extreme confidence with a hot-blooded, occasionally arrogant streak, especially concerning Mazinger Z's power; he reacts confrontationally when its effectiveness is questioned. Beneath this lies a strong protective instinct toward his younger brother Shiro, associate Sayaka Yumi, and other allies, including a willingness for self-sacrifice.

Koji lives with his grandfather Juzo Kabuto and brother following his parents' presumed deaths. After Dr. Hell murders Juzo, Koji takes control of Mazinger Z, vowing to fight Dr. Hell's forces. Though his piloting skills were initially unrefined, he mastered Mazinger's operation rapidly across diverse battlefields. Beyond mecha combat, he shows proficiency in motorcycle handling and uses an unconventional fighting style targeting physical weak points, sometimes employing a photon gun.

In the Mazinger Z vs. Devilman narrative, Koji's encounter with Devilman starts contentiously. After Mazinger Z's battle accidentally frees the demon Sirene, Devilman (as Akira Fudo) mocks Mazinger's inability to fly, sparking a competitive motorcycle race. This rivalry shifts to cooperation when Dr. Hell allies with the Demon Tribe. During an attack targeting Mazinger's new Jet Scrander flight system, Koji witnesses Akira transform into Devilman to save Shiro and Sayaka from Sirene, establishing mutual trust. They then coordinate a defense against the combined forces of Dr. Hell and the demons. Koji ultimately pilots Mazinger Z using the repaired Jet Scrander into aerial combat, freeing the captive Devilman and defeating the demonic threat.

Across broader media, Koji's character evolves. After Mazinger Z's destruction against the Mycenae Empire, he reemerges in Great Mazinger with cybernetic enhancements, supporting Tetsuya Tsurugi. Later, in Grendizer, he transitions to a secondary role as Duke Fleed's ally, designing combat aircraft like the Double Spazer; this shift sometimes places him in rescue scenarios.

His relationships feature a combative yet caring dynamic with Sayaka Yumi, frequent conflicts with the comedic Boss, and mentorship under Professor Gennosuke Yumi. A core element is inheriting Mazinger Z from his grandfather, coupled with the warning that piloting it could make him "a God or Devil," highlighting the responsibility accompanying its destructive power.

Koji's combat legacy includes popularizing the vocalization of attack names during battles, such as Rocket Punch and Breast Fire.