Ru Casel stands as the central antagonist, wielding overwhelming power and radiating an intimidating presence that isolates others, thus earning the moniker "Dark Dragon of Destruction." His racing motivation centers on deriving satisfaction from opponents' grief and despair in defeat. He infiltrates the Gurao racing school under false pretenses, joining as a trainee despite resistance from existing members. His background identifies him as the "child sent by a black hole," an entity destined to consume and banish all existence into darkness, with the ultimate objective of universal annihilation through destructive energy.

His power draws from negative emotions—anger, hatred, and destruction—amplified by victories over other racers. Specific abilities include generating blazes or fire from his hands and triggering monstrous transformations in others by augmenting their power. Recognizing psychological similarities with the racer Shiro, he strategically cultivates their connection to manipulate Shiro into undergoing a werewolf-like transformation capable of freezing surroundings.

Physically, Ru Casel has blue-green eyes marked by distinctive red half-bow tattoos beneath each. Long brown spiky hair frames his sharp-browed, aesthetically proportioned face, extending to his cheeks and neck, and reveals prominent sharp teeth. His muscular physique complements a gray sleeveless vest adorned with dual orange dragon motifs over blue clothing, accessorized by striped wristbands, knee-high white-and-dark boots, and a waistband housing racing equipment.

The narrative culminates in a decisive confrontation where multiple racers unite against his universal destruction agenda during a final race. This conflict resolves with his permanent defeat through mortality.