Arthur infiltrated Camelot castle, searching for the Holy Sword, Excalibur. When he entered, he was immediately found by Zeldris and Cusack, and then escaped while Cath distracted them. After that, Meliodas and Chandler appeared, joining Zeldris and Cusack who had beaten up Cath. An enraged Arthur then takes out Excalibur and starts the fight.
Arthur decides to take on the four demons, stating that he is going to to defeat them and reclaim the kingdom. Chandler makes the first move, using Exterminate Ray on Arthur at point-blank range. Then, Chandler's head is suddenly chopped off. Arthur reveals himself unscathed. In a quick movement, Arthur severs Cusack's left arm to retrieve Cath. Before Cusack could react, Arthur performs a big slash cutting the demon in half, followed with a flurry of sword swings so strong that destroys the walls of the castle.
While Arthur is comforting Cath, Zeldris attacks him from the back. But the king block it and many following attacks as well, without even looking back. Zeldris recognizes this technique as Mumyo no Mai, a technique used by a blind human swordsman of yore. Arthur swiftly counter Zeldris with the Deathpecker technique, that involves consecutive lunge attacks. Zeldris recognizes this as well as a technique by the War King Tartenos. Meliodas also recognizes the initial techniques as belonging to the human Master Swordsman Carfen. The battle continues with Meliodas and Zeldris teaming up against the Arthur, who avoids all attacks, slashing the brothers in the process.
Arthur thinks he defeated them, but the four demons reappear, unscathed. Cath asks a shocked Arthur if his magic power has awakened yet. Arthur confirms that he did not, and proceeds to recommence his assault. In that moment, the four demons projects their huge evil auras, stopping Arthur in his tracks. Sensing the impending doom, Cath telepathically communicates with Merlin.
Suddenly, Excalibur becomes heavy, falling to the ground. Because of the great amount of magic the sword required, Arthur became unable to move. Cusack took advantage of Arthur and after lecturing him, he uses an ability called Resonant on him. While the demon decides what to do with him, Merlin teleports in and immobilizes Cusack with an ice spell. Meliodas orders the mage to hand over the Faith commandment that is in her power. Merlin refuses, telling him that as he is working to become the Demon King, his lover and friends are putting their lives in risk in order to save him. As Cusack is freeing himself from the icy prison, Merlin takes Arthur and Cath back to the Boar's Hat.