Kouji Kabuto, a supporting protagonist, returned to Japan after studying aerospace engineering abroad, focusing on unidentified flying objects. He had previously piloted Mazinger Z against Dr. Hell and the Mycenean Empire. Upon his return, he joined the Space Science Laboratory. He designed and constructed his own flying saucer, the TFO (Terrestrial Flying Object), intending to initiate peaceful first contact with extraterrestrial life, reflecting his optimistic view. His perspective shifted drastically after encountering hostile Vegan forces. Rescued during an initial Vegan attack by Duke Fleed piloting Grendizer, this encounter revealed both the alien threat and Duke’s true identity. Kouji's personality retained traits like stubbornness, directness, and a hot-blooded approach to conflict, often charging impulsively into battle with the TFO despite its limited combat capability. However, he demonstrated increased maturity, showing greater openness to collaboration and strategic reasoning. Recognizing the Vegan threat's severity, he vowed unconditional support for Duke Fleed. Initially, his combat role involved piloting the TFO for reconnaissance and light support. After the TFO's destruction, he designed and piloted the more advanced Double Spazer, a jet-like machine with enhanced weaponry. The Double Spazer could attach to Grendizer, providing flight capability and supplementary firepower during battles against the Vegan Empire’s saucer beasts. His engineering skills proved vital beyond piloting, contributing tactical and technical support to the team. His relationship with Duke Fleed evolved from initial friction to deep camaraderie. Despite differing temperaments—Duke being more reserved and battle-weary—they developed mutual respect and functioned effectively as allies, exemplifying a "Bash Brothers" dynamic during combined assaults. Interactions with other characters, like Hikaru Makiba, remained marked by straightforwardness and occasional abrasiveness. His commitment to protecting Earth never wavered. He participated in the final battle against King Vega’s forces, contributing to the decisive victory. Following the conflict, he departed Earth alongside Duke and Maria Fleed, traveling to planet Fleed to aid in its reconstruction efforts, concluding his involvement.