Arthur is the central protagonist in the anime adaptation of Arthurian legend. As an infant prince during his father Uther Pendragon's rule, Camelot falls under attack by the malevolent King Lavik. The magician Merlin rescues the infant Arthur, entrusting him to a knight for protection. This knight raises Arthur as his own son, concealing the protagonist's royal lineage throughout his childhood.

At age 15, Arthur witnesses a tournament alongside his foster father. During this event, he draws the sword Excalibur from a stone—a decisive act proving his divine right to rule England as its legitimate sovereign. This revelation compels his foster father to disclose Arthur's true heritage as Uther Pendragon's heir, leading Arthur to assume his role as king.

Arthur's primary objective becomes opposing King Lavik and the witch Medessa, the forces threatening the kingdom. He leads his loyal subjects in this conflict, uniting various knights under his banner. The narrative focuses on Arthur's quest to locate the Holy Shield, depicted as the sole artifact capable of defeating Lavik and unifying the realm. Merlin serves as Arthur's advisor and mentor, providing magical guidance and strategic counsel throughout this struggle.

Arthur's leadership unites prominent knights, including Lancelot, Tristan, Percival, and Galahad, who join his cause against their common adversaries. While Sir Kay is counted among Arthur's knights, their specific relationship dynamics remain undefined. Arthur's journey traces his growth from ward to sovereign rallying his forces against tyranny, driven by the mission to secure peace through the Holy Shield's recovery.