Braiking Boss is a central figure in the narrative, serving as the former ruler of the robot army that once dominated the world. His background is defined by a long period of absolute power, during which robots subjugated humanity. The arrival of a mysterious girl named Luna, who was summoned by humans as a potential source of salvation, was perceived by him as a direct threat to his rule. In response, Braiking Boss ordered three of his most powerful cyborg warriors, including his subordinate Casshern, to assassinate her. This decision proved catastrophic, as the successful killing of Luna triggered the Ruin, a cataclysmic event that brought about the end of the world. The Ruin caused the planet's atmosphere to become poisoned and stripped robots of their effective immortality, causing them to slowly rust and die.

In the desolate world that follows, Braiking Boss is no longer a powerful emperor but a wanderer observing the consequences of his actions. He is an imposing figure, typically seen in a tattered cloak that hides much of his form. His physical appearance is striking and severe; he has a bald, metallic head and his face is partially covered with synthetic skin, while the other half is featureless black metal with visible bolts. A single red eye is perpetually visible, giving him a leering and calculating expression. Despite his fall from power, his personality is defined by a kingly and resolute perspective. He does not seek to reclaim his former empire or eat Casshern to gain eternal life, dismissing such rumors. Instead, he demonstrates a strong, consistent sense of responsibility for his followers, believing that a leader must bear the suffering of his subjects as a weight upon himself. This is shown in his final days, where he takes the time to dig graves for his fallen robot troops, finding peace only once this duty is complete.

Braiking Boss's role in the story is that of a shadowy observer and the architect of the world's suffering. He spends much of his time following Casshern from a distance, silently watching his former subordinate's journey and actions. His primary motivation shifts from maintaining power to a form of atonement and acceptance of judgment. He recognizes that he is the true cause of the world's destruction, and his goal becomes to witness the resolution of the events he set in motion. His key relationships are defined by his past. He is the former master of Casshern, Dio, and Leda, having sent them on the fateful mission to kill Luna. The scientist Ohji, who created Casshern as part of an experiment, was also a scientist who worked under him. These relationships are built on a foundation of command and the heavy, often tragic, consequences of his orders.

Throughout the series, Braiking Boss experiences little change in his demeanor or core beliefs, but his situation evolves toward a final resolution. He is not interested in salvation for himself. At the end of the story, he and his remaining army find Luna, but when Casshern arrives, Braiking Boss engages his former soldier in a fight that moves at his own slow, deliberate pace. He is defeated, and his final request is for Casshern to kill Luna, a command that reflects his unwavering belief in accepting responsibility. He feels content in his death, viewing it as a form of divine retribution for his sins and a long-overdue justice for the ruination of the world. In terms of notable abilities, as a powerful prototype robot commander, Braiking Boss possesses immense physical strength, agility, and durability far superior to a human. His movements are described as slow, sturdy, and fluid, yet he is capable of cutting down anyone who stands before him, making him a formidable opponent even at the end of his existence.