Prince Jordy Volder, known as Jojo, serves as the central protagonist. His life begins amidst the fall of House Volder's three-thousand-year reign, shattered by the conqueror Marder's invasion. As a newborn prince, he witnesses Marder's forces kill his father, King Volder, and capture his mother, Queen Felia. The royal guard captain Asbeth rescues the infant, fleeing into exile. Asbeth raises the prince under the alias "Jojo," evading Marder's hunters across the medieval planet Arst, posing as his grandfather. Their hidden mission involves seeking the legendary iron colossus Galient, prophesied to manifest under evil's rule.

During twelve years in exile, Jojo forms a close childhood bond with Chururu, daughter of a White Valley resistance leader. Their connection deepens into a romance characterized by frequent arguments, visible mutual crushes, and eventual marriage. Jojo's defining moment arrives when he and Chururu discover the buried Galient within a cave system. Upon encountering the colossal mecha, Jojo enters a trance-like state, instinctively grasping its piloting controls despite no prior experience. This awakening coincides with the arrival of Hilmuka, a human alien enforcer from a galaxy-spanning policing entity, who becomes his mentor. As the sole pilot of Galient, the twelve-year-old Jojo becomes a child soldier, spearheading the resistance against Marder's empire. He shoulders wartime burdens while driven by the goal of rescuing his mother, imprisoned in crystalline suspended animation as Marder's trophy.

Jojo exhibits an adorably precocious nature, displaying unexpected focus and combat prowess for his age. Galient functions as an empathic weapon, autonomously reacting to shield him during emotional distress. Throughout the conflict, he confronts Marder's forces, including the tyrant's dragon Hy Shaltat, and navigates political intricacies involving Hilmuka's non-interference directive and Marder's ambitions beyond Arst. The narrative concludes with Jojo participating in Arst's mass evacuation before the planet's annihilation by the Eraser weapon. The ending depicts him embracing Chururu, holding Galient's sword amid blowing rose petals.

In the OVA "Crest of Iron," Jojo is reimagined as an eighteen-year-old, presented as Mardoul's biological son alongside siblings High Schultat and Chururu. This version significantly alters his background, placing him within Mardoul's family during a rebellion sparked by High Schultat's excessive brutality. While still piloting Galient, this iteration explores divergent familial dynamics and conflicts.