Charles Arbor is a significant antagonist in the story, serving as the eldest son and heir of the powerful Arbor Duke family within the Beltrum Kingdom. He initially holds the prestigious position of vice-commander of the Royal Guard, a role that fuels his sense of entitlement and superiority. His background is steeped in the privileges of high nobility, and he views commoners with contempt and other nobles as either tools to be used or rivals to be put down. This worldview is central to his identity, as he believes his status automatically makes him superior in every way to those beneath him, particularly people of common birth or those he perceives as threats to his ego.

Charles Arbor's personality is defined by a volatile combination of arrogance, impulsiveness, and deep-seated insecurity. He is prone to violent outbursts and makes hasty, emotion-driven decisions to protect his pride and position. Beneath his noble facade lies a corrupt and self-serving individual who lacks the chivalric ideals associated with knighthood. He wholeheartedly believes in his own importance and is unable to admit his mistakes, often making rash choices that lead to his downfall. A key facet of his personality is an intense inferiority complex; he detests anyone he considers more skilled or talented than himself, such as the fellow knight Alfred Emerle, and uses his higher rank to belittle them. This insecurity also manifests as a possessive obsession, as seen when he forces Celia Claire into an engagement and deludes himself into believing she genuinely loves him.

His primary motivation throughout the story is the preservation and aggrandizement of his own status and power. He is driven by a desperate need for recognition and a desire to wash away the shame of his past failures. His actions, from falsely accusing an innocent person to plotting political marriages, are all calculated to secure his standing and feed his hunger for dominance. He is also deeply motivated by a personal vendetta against Rio (also known as Haruto Amakawa), who has been a source of repeated humiliation and a direct obstacle to his ambitions. Whether seeking revenge for a public defeat or trying to thwart Rio's interventions, Charles's actions are consistently guided by his wounded pride and his instinct for self-preservation.

In the story, Charles Arbor initially serves as a symbol of the corrupt nobility that plagues the Beltrum Kingdom. His role is that of an antagonist whose actions create conflict for the protagonist, Rio. He is first seen abusing his authority when he tortures a young Rio, attempting to force a false confession for the kidnapping of Princess Flora, an event for which he is later demoted. Years later, he attempts to publicly humiliate and injure Rio during a training match but is instead defeated in a single blow. After his family regains political power through a secret pact, he orchestrates the coerced engagement of the brilliant mage Celia Claire to use her as a hostage, a plan that Rio foils by kidnapping Celia. His role evolves as he becomes an unwitting pawn for the shadowy manipulator, Reiss, who uses Charles's ambition to further his own schemes. Charles leads the forces hunting for the escaped Princess Christina, only to be captured by Rio and handed over to the Restoration faction as a prisoner of war.

His key relationships are largely antagonistic or transactional. His relationship with Rio is one of profound and bitter rivalry, beginning with an act of torture and escalating through public defeat and foiled schemes. Charles harbors a deep, irrational hatred for Rio, who has consistently humiliated him and obstructed his plans. In contrast, he views Celia Claire as a possession, a prize to be won to secure his family's power and satisfy his ego, and he is blind to her revulsion. He is envious of Alfred Emerle, a more capable and honorable knight, constantly trying to undermine him due to his own inferiority complex. His relationship with the merchant Reiss is one of manipulation; Charles believes he is a partner in power, but he is ultimately just a tool in Reiss's larger political games, a fact he only comes to realize after his capture.

Charles Arbor experiences a notable arc that traces his fall from grace and his desperate, often misguided, attempts at redemption. He begins as a powerful noble and commander, but his corrupt and impulsive choices lead to his demotion and public disgrace. Upon regaining influence, his schemes are repeatedly thwarted, culminating in his capture and imprisonment. During his interrogation, he is forced to confront the reality that he has been nothing more than a pawn for Reiss, having no knowledge of the deeper conspiracies at play. This moment of clarity marks a turning point. After negotiations lead to his release, his drive shifts from personal glory to the pursuit of familial redemption. He joins a dangerous assault force led by Renji Kikuchi, serving as the vanguard in an operation to retake the city of Rodania, hoping to restore his lost honor. Though his legacy remains stained by his past ruthlessness, his character arc moves from an entitled villain to a disgraced figure struggling to atone.

Regarding notable abilities, Charles Arbor is described as being average in every aspect of combat and command. His original position as vice-commander was not earned through exceptional skill but was a product of his noble privilege. This mediocrity is a source of his deep-seated insecurity, as he is constantly overshadowed by genuinely talented individuals like Alfred and Rio. His lack of significant ability is most clearly demonstrated when he is defeated by Rio in a single, effortless counter during a public duel, highlighting that his power lies in his political title and family name rather than any personal prowess.