Kouji Kabuto is the protagonist of the show, an average student with great skill in driving motorcycles. He lived with his brother Shiro and his grandfather Juuzo, after his parents were apparently killed in a lab accident caused by his grandfather.
One day, Koji receives a call from his grandfather to meet him at his mountain cabin. Just as Kouji arrives however, the cabin explodes. Searching the remains, he uncovers a hidden doorway into the mountain and inside, he finds his dying grandfather who tells him with his dying wish to pilot "Mazinger Z" and stop a man named Dr. Hell.
Kouji continues into the hidden lab and discovers the huge, humanoid robot Mazinger Z, and the hover pilder which is used to control it. Honoring his grandfather's last wish, he joins up with the Photon Power Labs and fights the forces of Dr. Hell with his Mazinger Z.
A supporting character, primarily acting as back up for Duke Fleed, the series protagonist. He enters the war against the Vegan Empire with Duke Fleed and his allies. He initially pilots the TFO, a small recon unit with minimal battle capacity. Later, he fights more directly alongside Duke with the Double Spazer, a jet-like machine with greater firepower that attaches itself to Grendizer and grants it flight capability ala the Scrander.
His personality is reminiscent of how he is portrayed in the original Mazinger Z anime. He is stubborn, hot blooded, direct, and confrontational. However, he has matured a bit, as was evident in Great Mazinger. He is still likely to be the first to charge into battle, but is more open to reason now.
The protagonist of the series. Kouji lives with his younger brother Shiro and his grandfather Juuzo in their manor in Atami. Though his grandfather caused the accident that apparently killed his parents, Kouji feels no ill-will towards him and in fact holds him in high regard, attacking anyone who dares insults his grandfather.
During the Ashura Corps first attack on Atami, Juuzo sends out the hover pilder to Kouji and tells him to use it to quickly fly home. Just as he reaches the manor, it is utterly obliterated as Juuzo sends out his life's work from his underground lab, the super robot Mazinger Z. After docking the pilder with Mazinger's head, Juuzo tells Kouji that with Mazinger, he has the power to do anything he wants with the world—he could even become a god or the devil. As the ultimate penance for accidentally killing his parents, Juuzo will make his grandson superhuman. Having been granted this new-found power, Kouji decides that he will use it to fight the Kabuto family's long-time enemy—Dr. Hell—and his army of mechanical beasts.