Excalibur

Excalibur is a longsword that was originally wielded by Uther Pendragon, then Arthur Pendragon after him. Over several generations, the sword has become inextricably connected with Arthuria and the Pendragon family, to the point that the kingdom's coronation ritual involves the sword directly.

Description
Excalibur, at first glance, seems to be a mundane, if finely decorated, longsword. Its blade is made of an unknown, steel-like alloy, and is embossed with an inscription on one side. The hilt is golden, and the pommel is decorated with seven gemstones on either side; the largest stone represents the people of Arthuria and its neighboring lands, while each of the remaining six, arranged in a ring around the largest, represent one of the six gods.

Excalibur's uniqueness is in its magical properties. The sword is particularly damaging to "corrupted" entities such as demons and the undead, to the point that even touching it will burn them. It also cannot be damaged or dulled by ordinary means, allowing it to maintain its sharp edge and otherwise remain pristine for centuries without any maintenance. Its most renowned property, however, is its tie to the Pendragon bloodline. If one is not a direct descendant of Uther Pendragon and tries to directly lift the sword (e.g. by the hilt), they will find it far too heavy to move in spite of its actual weight or their own strength. Thus, only true-blooded Pendragons are capable of wielding Excalibur.

History
During the First Crystal War, Excalibur was forged for the knight and rebellion general Uther Pendragon. As a show of trust and respect towards him, and to prevent the sword's power from being abused should it fall in the wrong hands, it was given a powerful enchantment so that only Uther could wield it. He kept the sword by his side at all times, using it on the battlefield and effectively turning it into a symbol of the rebels' cause. The sight of the sword and its owner became feared by the Mercian forces, including a particular Shadowknight that fought on the front lines (though it should be noted he feared the sword for its enchantments, not for Uther or his merit). However, despite his competence and the sword's power, Uther would be fatally wounded in the final battle of the war. In his final moments, the knight inadvertently planted the sword in a large stone while trying to right himself and keep fighting.

Due to its enchantment, once Excalibur was planted in the stone, not even the strongest of the rebels could draw it. The sword, still embedded in the stone, was moved to a small memorial outside of Camelot. Around this time, a prophecy arose that the next person to draw the sword would become king of Mercia. This led many to attempt to remove the sword from its stone; however, all of them failed. It seemed that the sword would remain where it was, unable to be used, for the rest of time. However, one day, a young farmhand named Arthur noticed the memorial and, purely out of curiosity, attempted to pull Excalibur out of its stone. Unlike those before him, he managed to draw the sword, with a nearby Psychic bearing witness. She approached Arthur, explaining the sword's importance and convincing him to become a knight. The boy decided he would put the sword back, but planned to return once he was able to properly wield it. Consequently, Excalibur remained planted in its stone for several more years, but Arthur remained true to his word. Near the end of the Second Crystal War, a grown Arthur returned and drew Excalibur, eventually using it to kill the leader of the Quartizine Order.

Once the Second Crystal War was over, Arthur was crowned king of Mercia. As king, he kept the sword within arms' reach at all times, even when bathing or sleeping. On his deathbed, though, he ordered that the stone from Uther's memorial be brought to him. Once the stone was in his presence, he returned Excalibur to it, stating that his heir would need to pull the sword back out, just as he had decades before, to prove their right to rule. This started a tradition that became part of the kingdom's coronation ritual, solidifying Excalibur as a symbol of the Pendragon family and the kingdom they now ruled over. Its connection to the Arthurian monarchy has become so strong that, when a paladin accidentally drew the sword many years later, he was immediately expected to become king.

Trivia

 * Needless to say, Excalibur draws heavy inspiration from its namesake in Arthurian legend. Its inability to be wielded by anyone outside the Pendragon family is in reference to the legend of the "sword in the stone."