Emeraldas fled her homeworld, La Metal, as a child after its ruler, Queen Promethium, transformed it into a mechanized planet, resulting in the horrifying destruction of its organic life. Her brutal early years adrift in space, marked by hardship and exploitation, forged her cynical view of humanity and an unyielding drive for survival and independence, costing her left eye, now covered by a distinctive eyepatch.

Commanding the massive pirate battleship *Queen Emeraldas* single-handedly, she cuts an imposing figure recognized by her long black cape, eyepatch, and powerful energy pistol, the Cosmo Dragoon. She reigns as a solitary and feared space pirate queen, governed by a strict personal code. Emeraldas annihilates those she judges truly evil or cowardly, especially predators of the weak, yet shows respect and occasional mercy to individuals demonstrating genuine courage, conviction, or nobility, even adversaries. She values freedom above all, refusing to be bound.

Her relationship with her sister, Maetel—another daughter of Queen Promethium—is complex and adversarial. While Maetel serves Promethium's agenda aboard the Galaxy Express 999, guiding souls to her, Emeraldas utterly rejects their mother and views Maetel's mission as complicit in Promethium's tyranny. She frequently confronts her sister, seeing their paths as fundamentally opposed, yet a deep, unbreakable bond persists between them.

Emeraldas often aids or observes individuals, particularly young men like Hiroshi, who embody the courage she respects. Her actions, though brutal, align with her personal justice, eliminating threats such as corrupt warlords and slavers—manifestations of the evil she despises. Her existence is marked by perpetual solitude and conflict, defined by her traumatic past, absolute rejection of Queen Promethium's philosophy, unwavering personal code, and enduring, complex connection to Maetel. She remains a powerful, independent force operating on the galaxy's fringes.