This page describes the Koji Kabuto seen in the Toei Animation television series. For other versions of the character, see: Koji Kabuto (Disambiguation).
Koji is famous for breaking the mold of main characters of his time, being hot-blooded and arrogant but learning sense as the series progressed.
Koji is a teenager of average height with an athletic build, black eyes, broad eyebrows, and black spiked hair that is combed back along with forward facing sideburns.
Koji and his brother, Shiro Kabuto, were raised by their grandfather after their parents were killed in a laboratory accident. After Juzo started to obsessively work on a secret project, a housekeeper named Rumi was hired to take care of them. By the time Koji got into high school, he spent most of his free time riding his motorcycle earning him a reputation as a skilled biker.
Koji is hot-blooded, impulsive, bratty, reckless and over-confident. His personality often puts him in trouble during his fights and gets him into arguments with Sayaka. His recklessness also extends to his belief in road safety, as he narrowly avoids stop light through motorcycle stunts. His proud and headstrong nature makes him unwilling to back down from challenges, even when he is at a disadvantage. His pride also extends to Mazinger Z. He easily becomes upset whenever someone seems to doubt the robot's power.
Initially he was very cocky and rude, even when talking to his friends. Koji often criticized Sayaka for her tomboyish and started arguments over petty reasons. In one such occasion, he ripped Sayaka's shirt open and poured the soup she made for him simply because he didn't like the taste. As the series progresses, Koji shows signs of growth by giving more though to his actions and showing Sayaka a little more respect. Despite being vehemently against the idea of upgrading Aphrodite A in the early episodes, Koji was the most vocal supporter of the proposal of building Diana A as a combat robot later on.
Beneath his rough exterior, there is a compassionate side Koji reserves to his loved ones. As his grandfather became wrapped in his work, Koji became more protective of Shiro. Similarly, his attitude towards Sayaka - attempting to dissuade her from joining him in battle with inflammatory remarks - could arguably also be attributed to him being protective in his own way.
Koji's most famous trait is calling out loud the names of Mazinger Z's attacks, occasionally even doing the movements the Mazinger makes to execute them. This is mainly Go Nagai's way of bringing robot and pilot together as one.
Koji cares deeply about his family with the death of his parents and the eventual estrangement between him and Juzo. However, Koji still loved his grandfather and keeps Mazinger Z as a precious memento of him. With Juzo's death Koji became determined to avenge his grandfather by fighting Dr. Hell and his Mechanical Beasts. With Shiro being Koji's only living blood relative, he became very protective of his little brother; not wanting Shiro to get involved in any fights with Dr. Hell. He also encourages Shiro to take risks including his crush on Lorelai. In Great Mazinger, Koji reunites with his father who everyone believed was dead which brought relief to Koji, but the reunion was short lived when Kenzo died in an attack by Great Marshall Hell. Koji also bonded with Kenzo's adopted son Tetsuya Tsurugi, especially after their father's death.
Despite arguing fairly often, Koji shares a solid friendship with Sayaka. Most of their squabbles involve Koji's disapproval of what he judges to be un-lady like on Sayaka's part, Koji's overall recklessness and brash personality or other trivial matters. They usually are quick to forgive each other, but sometimes their fight manage to escalate to the point one of them refuses to help the other during battles. Following Koji's decisive vote against the proposal to have Aphrodite A upgraded, a fight broke out between between the two which resulted in Koji initially refusing to aid Sayaka in the battle against Abdora U6.. Similarly, after a misunderstanding resulted in an all out brawl, Sayaka declined Koji's request for help.  Koji is aware of Sayaka's feelings towards him and often teases her about it. Although he sometimes appears to show interest in her, even competing with Boss over it, they relationships stays platonic until the end. Sayaka's feelings are more explicit; Whenever Koji appears to show interest in another girl, she becomes visibly jealous. Koji's fondness over Misato being the main reason Sayaka didn't like her very much at first.
Koji's criticism toward Sayaka and Boss' performance in battle and overall lack of gratitude towards their help often push them to join forces in an attempt to show Koji up. As the series progresses, Koji is shown to be have more appreciation towards his friendship with Sayaka and Boss. The most notable instance of his change being his support over Diana A being built as combat robot as early in the series he was against the idea of Sayaka having a stronger robot.
Since their first meeting, Koji is shown to be interest in Misato. Compared with his relationship with Sayaka and Boss, Koji treats Misato much better and quickly becomes good friends with her.
Boss has a mostly one-sided rivalry. While Koji gets annoyed with Boss from time to time, he is mostly happy to oblige and compete with him. Their rivalry also manifests when battling Mechanical Beast. Even after Boss Borot shown to be outmatched time and time again against the Mechanical Beasts, Boss doesn't give up trying to show Koji up often joining forces with Sayaka to that end. When Koji returns in the final episodes of Great Mazinger, Boss offers to join forces with him so they can try to show up Tetsuya together instead.
Even though Koji mocks Boss' clumsiness and poor performance when it comes to piloting, the two of them are good friends. During the series, they are shown to partake in different activities together and are always willing to fight for each other's sake. When Koji was incapable of sorting following a serious injury, Boss offered to fight in his place even knowing he stood no chance against the Mechanical Beast in question. Before leaving, Boss asks Dr. Yumi to tell Koji he is his best friend if he doesn't make it. 
As he is interested in Sayaka, the fight over her attention sometimes ends up being a point of contention between the two. Whenever Koji and Sayaka have a squabble, Boss reprimands him and tries to gain her favor by giving his support.
Koji was very close to Dr. Morimori. The two of them appear to have shared a friendship ever since Koji was still a child. His death at the hands of the Iron Cross soldiers left Koji enraged. He is shown paying respects at Morimori's grave a few episodes later.
Despite butting heads over their different mindsets, Koji and Duke grow to become good friends as the series progress. They go on to help each other during the fight against the Vegan Empire's forces and once the war is over, he expresses sadness seeing his friend return to his home world.
Upon first meeting her, Koji had an infatuation with Maria Fleed despite having already existing interests in Sayaka. Maria herself has a very similar personality and dynamic as Sayaka had with Koji, often caused by her disapproval of Koji's overall brashness but like Sayaka, the two are usually are quick to forgive each other. In Dynamic Heroes, his infidelity came to a breaking point as upon finding out about his affair with the Fleedian Duchess, Sayaka made her disdain for Maria unequivocally clear for stealing Koji from her, but by the end of the saga she grows to begrudgingly accept her, despite expressing her resentment towards Koji for cheating on her.
One day Koji returns home to learn that Rumi, the housemaid, has been murdered. After receiving the bad news from his grandchildren, Juzo Kabuto summons Koji and Shiro to his house in the woods. They arrive to find the building already blown up. While searching for signs of their grandfather, the brothers stumble in the stairs leading to Juzo's underground laboratory. There, they find their grandfather mortally wounded. Before passing away, Juzo tells them about Dr. Hell's involvement in his death and reveals his greatest invention: Mazinger Z. After boarding the robot, Koji goes on to meet Sayaka and Dr. Yumi and starts his struggle against Dr. Hell's Underground Empire and his army of Mechanical Beasts.
One after another, Dr. Hell sends Mechanical Beasts to attack Japan, with the Mazinger fighting and defeating them with assistance from Sayaka and her mechs. Once Koji and company encountered a mech originally designed by Juzo but built by Dr. Hell, Minerva X which although neither enemy nor ally showed attraction to the Mazinger. However she end up getting destroyed by Sayaka after falling under Hell's control. With most of her body still intact, Koji had Mazinger Z carry her to the ocean promising to one day bring her back. 
In one fight with a Mechanical Beast, Koji was severely injured after Sayaka refused to help him following a earlier fight between the two. Bazuson M1 survives the fight and gets repaired before Koji recovers. As the Mechanical Beast is on its way to run over a children's hospital, Sayaka decides to atone by piloting Mazinger Z in Koji's place. After learning about it, a still injured Koji rushes to her side in Aphrodite A. The two of them change back to their respective robots and with help from Boss, manage to stop Bazuson M1 once for all. 
Following Baron Ashura's death, Koji decided to leave the Photon Power Laboratory to go fishing as he thought Dr. Hell's attacks would subside for a short while. He was wrong. Koji gets captured by a team of Iron Cross soldiers and ends up tied to a tree. As the Photon Power Lab was being attacked at the time, Dr. Morimori heads to Koji's fishing spot to bring him back to fight the Mechanical Beasts. The Iron Cross soldiers notice Morimori approaching and plant a landmine in the road. Despite's Koji attempts to warn him of the danger, Morimori drives over the mine and dies in Koji's arms. After vowing to avenge the scientist by killing every single member of the Underground Empire, Koji engages in a rage fueled battle against Jetfire P1 and Greeks ΨII. He almost dies in the process, but manages to destroy them both.
Eventually, Koji and friends decide to take the fight to Dr. Hell's island fortress. It is there that Koji finally avenges his grandfather by having Mazinger Z destroy the island and Gool with Dr. Hell and Count Brocken still on board. Although Dr. Hell was defeated, Koji was still worried as he knew Archduke Gorgon was still alive.
With the Underground Empire destroyed and the forces of good still recovering from the final battle against Dr. Hell, the Mycenaen Empire launch their first attack. Koji fights valiantly, but ends up being defeated by the Great General of Darkness' soldiers. The Warrior Beasts turn their attention to the Photon Power Laboratory, but before they are able to kill Koji's friends, they are destroyed by Great Mazinger and it's pilot, Tetsuya Tsurugi. Koji is taken to the Science Fortress Laboratory for treatment. After recovering, Koji and Sayaka are sent to America to continue their studies leaving Japan's safety in the hands of Tetsuya and Jun.
Before his actual return to Japan, Koji is mentioned several times. Shiro and Boss are shown thinking about him and the Mycenaens even manage to sneak packages and containers into the Science Fortress Laboratory more than once by claiming they are presents from Koji.His first appearance turns out to be a fake-out as Boss started having hallucinations about Mazinger Z rescuing him after receiving a hit to the head. 
Koji's actual return happens close to the end of the series. While the Science Fortress Laboratory was being bombarded and about to be destroyed, Dr. Yumi telephoned Koji to ask for Mazinger Z's help. Koji then proceeded to get into a plane, fly from America to Japan, parachute into the Photon Power Laboratory, deploy in Mazinger Z and arrive in the battle just in time to stop Demonika from destroying the fortress. After the crisis is dealt with, Koji reunites with his father and joins Tetsuya, Jun and Boss in the fight against the Mycenae Empire. 
Although Koji and Tetsuya got along just fine in the beginning, this changed as Koji grew closer to his father. Thinking Kenzo is unjustly favoring his biological son over him, Tetsuya begins to antagonize Koji. When Mazinger Z is first attacked during the final battle, Tetsuya initially refuses to sortie to help Koji. Shiro and Kenzo are able to change his mind, but his late deployment allowed a Warrior Beast to ambush him forcing Kenzo to sacrifice himself to save him.
With Jun and Boss' help, Koji is able to destroy the Warrior Beast attacking the Photon Power Laboratory and returns in time to witness his father's final moments. He then goes on to destroy General Ligern, General Draydou and General Hadias. Finally, with the help of Tetsuya and the other pilots, Koji is able to destroy Demonika killing a resurrected Dr. Hell and the remaining Mycenaean officers putting an end to the war.
After retiring from being a pilot, Koji developed the TFO and started trying to establish contact with extraterrestrial life. Taking notice of his efforts, the adopted son of the Space Science Center's director, Daisuke Umon, warns him that aliens may not be amicable to earthlings. Koji, however, ignores his advice. When he notices a group of flying saucers approaching the Makiba Ranch, he tries to contact them only to be shot at. The alien force, which turns out to be part of the Vegan Empire, gets destroyed by Grendizer.
During the chaos, Koji manages to take a quick glance at the robot's pilot. Koji immediately suspects Daisuke is his mysterious savior and goes to confront him. Daisuke tries to deny it, but Koji doesn't buy it. After Daisuke reveals his true identity as the alien prince Duke Fleed, Koji joins him in his struggle against the Vegan Empire. Together, they go on to face several Saucer Beasts being later joined by Hikaru Makiba and Maria Fleed
In the end, Duke and his allies defeat Great Vega and the remaining Vegan forces. Although Koji initially refuses to show up to say his goodbyes to Duke and Maria, he changes his mind and catches up to Grendizer in the Double Spazer moments before they leave Earth. Duke and Maria return to Planet Fleed and Koji is assumed to have returned to the Space Science Center to continue finding intelligent life.
Much like in the anime, Koji and Mazinger Z go on to fight against the invading Mycenaen Warrior Beasts. Although they were able to hold off the first wave of enemies, the second, leaded by General Juuma would have overwhelmed Mazinger Z if not for the intervention of Great Mazinger and Tetsuya Tsurugi. Together, the Mazinger pilots manage to win the battle before parting ways.
Koji is brainwashed by Barendos and is forced to reveal information about Mazinger Z and Great Mazinger. He manages to free himself in time to inform Duke about Great Mazinger's weak spot giving him the chance to incapacitate the robot. Koji boards Great and together with Grendizer they destroy Barendos and his forces.
In the span of ten years between the ending of Great Mazinger and beginning of Mazinger Z: Infinity, Koji started a relationship with Sayaka and became a lead scientist in the new Photon Power Laboratory. However, at some point, they had a falling out as Sayaka was unsatisfied with the rate their relationship was - or wasn't - progressing.
After being alerted about Infinity discovery, Koji visits the excavation site and finds LiSA inside the ancient robot. Not long after, a resurrected Dr. Hell and his minions attack Japan once again. Koji joins the fight first as a publicity stunt, but when it becomes clear the Japanese forces are unable to defeat the Mechanical Beasts by themselves, Koji brings back Mazinger Z out of retirement.
After an immense struggle, LiSA powers up Mazinger Z using Photon Energy from all over the world. Koji defeats Dr. Hell and his minions once again and makes up with Sayaka. The epilogue shows the two of them getting married and having a human version of LiSA as a child years later.
Equipment and Abilities
At the start of the series, Koji had a hard time learning Mazinger Z's control scheme. He needed to be coached by Sayaka and reminded of his weapons. Nevertheless, after familiarizing Koji is shown to be a very skilled pilot. He is also shown to be very proficient with other vehicles, like his motorcycle, the TFO and the Spazers.
- Motorcycles: Koji has always ridden motorcycles, usually to blow off steam or for rides with Sayaka when there is no danger. Even when there is danger, Koji is always focused and drives with great skill to get where he needs to be. Koji owns his personal custom bike known as the Kabuto Go.
- Hover Pilder: The control center for Mazinger Z. It's fast and armed with a few weapons. It is eventually destroyed.
- Jet Pilder: The new control center for Mazinger Z. Compared to the Hover Pilder, it is superior in every way.
Koji fights in an unorthodox fighting style, mainly focusing on dealing with and hitting opponents in sensitive areas. He is able to stay in a fight, even against armed opponents.
Suits and Weapons
Koji gained his original pilot suit from the Three Scientists. It is made with Super Alloy Z which offers protection against conventional weaponry. It has a holster for the Photon Gun and a helmet shaped after the Photonic Research Lab.
In Grendizer, Koji is given a new pilot suit, compared to the original black and red costume, this one is blue and has a mouthpiece.
Intelligence and Strategy
At the start of the series, Koji's brashness presided over everything including strategy and sometimes even common sense. He does not appear to be good at studying as shown in the original series where his teacher had concerns for his grades. Over time, he becomes more intelligent, thinking of good and accurate strategies including disabling Mechanical Beasts that have hostages, often on the fly. By Grendizer, he has created his own hovering vehicle, indicating that he is knowledgeable on engineering.
Kabuto is Japanese for 'Helmet' which fits Koji's role as the Mazinger Z's pilot as he docks a vehicle on top of the mech's head.
- The Toei version of Koji is notable for having piloted the most mecha out of any incarnations of the character, having piloted 5 of them in various forms of media.
- Koji was originally going to 18 for his ownership of a motorcycle. However, his age was reduced to 16, then changed 17 in later episodes.