Kazuya Ryuzaki serves as the central protagonist, his background and development unfolding against a backdrop of interplanetary conflict. Orphaned at age five after his father Isamu Ryuzaki, an Earth delegation scientist, died during failed peace negotiations with the alien Baam race, Kazuya was raised by Dr. Shinichiro Izumi at the Daimobic Base. Shinichiro became his adoptive grandfather and karate instructor, rigorously training him in martial arts. At fourteen, Kazuya suffered a severe accident that broke his vertebral column, nearly paralyzing him. He endured an arduous rehabilitation, pushing his body beyond medically presumed limits through sheer willpower to regain mobility and resume martial arts, ultimately achieving black belt mastery.

Kazuya pilots the giant robot Daimos using a motion-capture system that translates his karate techniques directly into the robot's combat movements. His fighting style incorporates numerous specialized finishing moves, such as the Reppu Seikenzuki (Deadly Gale Correct Fist Thrust), channeling extreme force through Daimos' fist to shatter enemy interiors. The robot's extensive arsenal—including melee weapons like the Twin Dragon Blades and Coiling Dragon Staff, projectile systems such as the Five Shooter metal blades, and elemental manipulators like the fire-generating Fire Blizzard or freezing Freezer Storm—operates precisely in sync with his physical commands.

Pacifistic and idealistic by nature, Kazuya steadfastly pursues diplomatic solutions and believes in the inherent goodness of all beings. His worldview is fundamentally shaped by his love for Erika, a Baam princess he encountered with amnesia after a spaceship accident. Despite discovering her alien heritage and the resulting hostilities between their peoples, his commitment to her never wavers. This relationship drives his actions throughout the conflict, attracting suspicion from both sides; Earth military leader Miwa brands him a traitor, while Erika's brother Richter views the romance as a betrayal of Baam pride.

Kazuya's character evolves through exposure to moral ambiguities on both sides of the war. He confronts corruption within Earth's military, exemplified by Miwa's genocidal tactics against Baam refugees, which triggers Kazuya's explosive rage when Miwa harms civilians. Conversely, he acknowledges noble individuals among the Baam, such as General Balbas, who sacrifices himself to aid Kazuya. These experiences deepen his resolve to bridge the conflict through empathy rather than force. His idealism is severely tested when Erika seemingly betrays him under duress from the Baam usurper Olban, causing profound heartbreak, yet he perseveres in peace efforts after deducing her deception.

Supporting relationships include his adoptive sister Nana, whose childhood crush evolves into acceptance of his bond with Erika; his best friend Kyoshiro, who provides aerial support via the Galva FX-II jet while good-naturedly teasing him about his devotion to Erika; and Shinichiro, whose guidance anchors Kazuya's moral compass. The resolution sees Kazuya facilitating peace between Earth and Baam following Richter's sacrificial act that averts planetary destruction, allowing Kazuya and Erika to unite unimpeded.