As a result, Nagai made him a delinquent most notably noted when the character is rude towards Sayaka Yumi and feels bad for his actions.

[1] According to Nagai, he had the idea for piloting a robot from watching frustrated drivers in a traffic jam, imagining a car that could sprout arms and legs and walk over the other vehicles.

According to Nagai the concept of Mazinger Z was: ""I didn't equate giant robots with weapons, I wanted to give a teenaged character a suit of armor that would turn him into a hero."

Katsuta claimed he wanted Koji to be "a cheerful boy, lively and passionate acting without reasoning" in contrast to the serious personality of Fleed.

[4] For the film Infinity, the staff brought back Koji as the lead with the intention of giving him a character arc where becomes closer with the rest members from the cast.

In his first appearances in both manga and anime versions of Mazinger Z, Kabuto is originally an average high school student whose only apparent skill is driving motorcycles.

He lives with his brother Shiro and his grandfather Juuzo, as his parents are both deceased (although a few years later Koji's father, Kenzo Kabuto, turns out to be still alive).

From a seemingly mindless, reckless, boyish scoundrel, he gradually develops into a fighter who's up to match his opponent's ever greater challenges, showing a growing sense of duty, and a courage to fight to his death, or close to that.

But it is in the Grendizer series that Koji shows off the quality of his brain power, when he introduces the mini saucer he himself designed during his study period at NASA.

In the second Mazinger-Z spinoff Grendizer, Koji is reduced to being a sidekick to the series' main hero Duke Fleed - a long stint that many Mazinger Z Japanese fans did not appreciate.

When this saucer gets destroyed once and for all, Koji designs a more powerful aircraft called the Double Spazer which gives him a much more active role in battle.

[7] In retrospective, The Fandom Post acclaimed how Nagai and Toei developed Koji as one of the first mecha pilots in anime history but, like ANN, felt that his personality was too rude, sexist and often fell into the villain's traps in most episodes.

Nevertheless, the site noted that Koji's character made the series a success based on how he was one of the earliest mecha pilots, especially in South America, where the Mazinger Z anime was broadcast in the 1980s.

[12] Mania Entertainment enjoyed the fights between the robots and found the story escalates quickly when Koji is defeated in the first episode by the enemy and goes missing-in-action until he comes back with the stronger Mazinkaiser.

In contrast to DVDTalk, Mania Entertainment enjoyed the handling of Koji and Sayaka due to both of them coming across as tsunderes since in the beach episode it was clear the two had feelings for each other.

[14] ANN criticized Koji's characterization in Infinity for coming across as "angsty" during the times the plot handles elements of who should keep fighting for humanity while discussing the idea of a weak society compared by the reviewer to a TV drama.

IGN liked how the film did not solely focus on Koji's return to fight Dr. Hell as it allowed more cast members to integrated to the main story in the process.

In regards to his encounter with his nemesis Dr. Hell, the site appreciated how well developed as the protagonist and his allies creates a new Mazinger Z, largely superior than the original.