Colonel Eldomain commands Arfessian military forces from a warship illegally bearing the exclusive Skull and Crossbones insignia, a violation that sparks immediate confrontation. He employs aggressive tactics, launching unprovoked attacks on civilian craft like the freighter carrying stowaway Hiroshi Umino, demonstrating ruthless dominance. Pursuing the freighter to the desert planet Daibaran after an encounter with the pirate ship Queen Emeraldas, Eldomain personally leads the hunt for the entity that challenged him. His volatile nature surfaces when he brutalizes the young Hiroshi Umino after the boy confronts him within a saloon evoking an Old Western town.

Initially retreating from Emeraldas when she publicly demands he remove the stolen insignia, Eldomain later returns piloting a fighter craft, strafing the exposed Emeraldas from the air. Facing resistance, he escalates by seizing numerous Daibaran townspeople, including Hiroshi, as hostages. He leverages these captives in an attempt to force Emeraldas into vulnerability and lure her into a decisive battle against his full fleet.

Eldomain participates in the culminating wider conflict involving Arfessian ruler Queen Baraluda, though his specific combat role against her remains undefined. Narrative progression implies his ultimate defeat. His actions directly precipitate Emeraldas presenting Hiroshi Umino with the Cosmo Dragoon pistol, an item once belonging to Tochiro, following the resolution of the conflicts he instigated alongside Baraluda.