Kouji Kabuto starts as an average high school student, skilled in motorcycle driving, living with his younger brother Shiro and grandfather Juzo Kabuto following his parents' apparent death in a lab accident. His life transforms when Dr. Hell's forces murder Juzo; with his dying breath, Juzo entrusts Kouji with piloting the super robot Mazinger Z to protect humanity. Initially reckless and hotheaded, Kouji struggles to operate Mazinger Z effectively, frequently clashing with ally Sayaka Yumi due to his impulsive and occasionally sexist attitude. His early motivation focuses solely on avenging his grandfather's death. Throughout the Mazinger Z series, Kouji evolves from a "mindless, reckless, boyish scoundrel" into a determined fighter, developing a strong sense of duty and willingness to face near-fatal challenges. His bravery compensates for Mazinger Z's vulnerabilities against Dr. Hell's mechanical beasts. This growth encompasses improved tactical skills and emotional resilience, though he retains iconic battle cries like "Rocket Punch!" and "Breast Fire!". His relationship with Sayaka gradually matures from constant conflict to mutual respect and hinted romance, while his protective instincts extend to Shiro and colleagues at the Photon Power Laboratory. In Great Mazinger, Kouji returns after an initial defeat, aiding Tetsuya Tsurugi against the Mycenaean Empire. His maturity deepens, shifting from personal revenge to protecting civilians. He demonstrates increased strategic thinking during battles, though his fundamental hotblooded nature persists. Later, he travels to NASA to study UFO technology, designing a mini-saucer upon returning to Japan. This period highlights his intellectual growth, though the saucer proves ineffective in combat. Grendizer reduces Kouji to a supporting role as Duke Fleed's sidekick. Initially piloting his fragile saucer, he requires frequent rescuing by Fleed until developing the more capable Double Spazer aircraft. His personality here contrasts with Fleed's seriousness, emphasizing cheerfulness and passion. This era shows Kouji's adaptability in non-leadership roles while maintaining his courageous spirit. Later appearances further develop his character. In Mazinkaiser, Kouji discovers the titular robot in a hidden lab after Mazinger Z's capture, wielding its immense power responsibly despite initial struggles. Shin Mazinger portrays a more aggressive version; his protectiveness over Shiro and grief over Juzo's death lead to near-lethal aggression against enemies and temporary hostility toward Sayaka. The film Mazinger Z: Infinity depicts Kouji a decade post-Mycenaean war as a scientist who returns to piloting when Dr. Hell resurfaces, blending his inherited intellect with combat experience. Kouji's family relationships shape his journey. He deeply respects Juzo, viewing Mazinger Z as his grandfather's legacy. He acts as a guardian to Shiro, balancing reprimands with unwavering support. His initially contentious dynamic with Sayaka evolves into partnership and romantic tension. Discoveries about his father Kenzo—initially believed dead but later revealed as a cyborg—add emotional complexity, particularly after Kenzo's sacrificial death. These connections reinforce his core drive: protecting others rather than seeking glory.