King Arthur's origins trace back to "Entaku no Kishi Monogatari: Moero Arthur", where Merlin rescued him as an infant. Raised by a retired knight, he proved his royal destiny at fifteen by wielding the sacred sword Excalibur from its iron stand, an act confirming his rightful kingship of Britain.

In "Moero Arthur: Hakuba no Oji", Arthur journeys under a concealed identity with four companions across a futuristic Arthurian realm. His quest focuses on defeating the antagonist Ziking. Along the way, he faces diverse challenges: confronting a bear-man entity, recovering stolen secrets, rescuing allies like Peet, overcoming supernatural threats such as a life-draining magical flower, and battling a fire-spurting dragon. These encounters showcase his adaptability.

His path is marked by key adversaries and mysteries, including encounters with imposters, the enigmatic Black-Horsed Knight, and figures like the Phantom Princess Ginebia. He protects allies from threats like pirate ships and navigates interpersonal challenges symbolized by the "Rose Flower which Scatters Love". His battles culminate in a final confrontation against the "Last Heir" before achieving victory.

Arthur's character development centers on demonstrating leadership through adversity while maintaining his concealed identity until resolving the conflict with Ziking within the 22-episode series.