Holy Sword Excalibur

«Holy Sword Excaliber» (聖剣エクスキャリバー), the «sword which cut all of steel and tree», is «ALfheim Online»'s strongest legendary weapon. It is the only weapon that surpasses the «Demonic Sword Gram».

Mythology
Excaliber was forged by the god of blacksmith Völundr. King of the Frost Giant tribe «Þrym» once transformed into a wolf and infiltrated Jötunheimr to steal it. He then threw Excaliber into «Urðr's Spring», a lake at the center of Jötunheimr where it impaled the World Tree and cut off its roots. At that moment, Jötunheimr lost the blessings from the Tree and quickly degenerated into a barren wasteland of frost. As the roots of the tree retracted to Jötunheimr's canopy, the frozen lake was pulled up along with the roots. Thus the large mass of ice reached the canopy of the world, where the ice dungeon was formed and later fashioned into Þrym's castle, Þrymheimr. The great sword Excaliber, after impaling the roots of the Tree, became stuck at the bottom of the ice structure, where it keeps it from melting and the roots of the World Tree from regrowing.

Fairy Dance Arc
The sword was first discovered by Leafa and Kirito during their adventure in Jötunheimr, when Leafa noticed a golden light at the bottom of an ice dungeon above the Great Void while riding on Tonkii. Using a distance viewing magic, she identified the light as the Holy Sword Excaliber, however, knowing that the dungeon was too difficult for them, the two did not use the opportunity to challenge the dungeon and instead used the nearby stairs carved in one of the roots of the World Tree to ascend back to Alfheim.

The Excaliber was first shown during the battle between Kirito and Fairy King Oberon. After Kirito used Heathcliff's system ID to revoke Oberon's administrative authorities, Oberon attempts to summon this sword with the use of a system command, but the system no longer responds to him. Then Kirito repeats the same system command to generate the legendary sword and gives it to Oberon to use during their battle, while Kirito chose to use his current sword. However, due to Oberon's lack of experience in battles, even the power of this great sword wasn't enough for him to lay even a scratch on the far more experienced Kirito, who easily defeats Oberon.

Caliber
After discovering that others players have found the location of the «Holy Sword Excaliber», Kirito forms a party to raid the Inverted Pyramid Dungeon again. Upon arriving at Jötunheimr, they discover that other players are massacring the Beast-type Evil Gods with the help of the Humanoid-type Evil Gods. At that moment, the NPC «Queen of the Lake» Urðr appears and requests them to remove «Excaliber» from the «Plinth of Þrymheimr» to stop Þrym from invading Alfheim.

With most of the Humanoid-type Evil Gods currently preoccupied, Þrymheimr is left far less defended than usually, allowing the group to get through the dungeon at record time. However, after the sword is removed from its pedestal, the castle of Þrymheimr begins to collapse and fall. To escape certain death, the group needed to immediately jump out of the castle and onto Tonkii. However, as the sword was too heavy and couldn't be stored into a player's storage until the completion of the quest, Kirito leaves it behind. But, before the sword falls into the Great Void, Sinon fires a «Retrieving Arrow» at the sword and successfully retrieves it, giving it to Kirito, under the condition that he always thinks of her when using the sword.

Trivia

 * Contrary to popular belief, «Excaliber» cannot be obtained as a quest reward, as the quest Þrym and the Frost Giant generals give reward the «Fake Sword Caliburn», a weaker version of the Excaliber, instead.
 * The traditional spelling of the sword across most text is generally "Excalibur (エクスカリバー)", with a "U". Shinon, who was head librarian during middle school and thus read a large number of books, noticing this brought up several points regarding this name change and wondered about the meaning of "caliber" from the gun-related meaning (the diameter of the valleys on the rifling inside a gun's barrel) to the meaning of "a man's capacity", or "a man with high capability." In the end, the discussion was interrupted regarding Kazuto's capability to treat everyone due to his payment (compensation) from the government, and he resolved to never use Excaliber for personal gain as it contained the 'caliber' of himself and his companions.