Excalibur

The is a mighty sword wielded by the king of the Kingdom of Camelot, Arthur Pendragon.

Appearance
Excalibur is a broadsword with a very wide blade. The grip has a dark swirly appearance to it, giving the appearance of a cosmic void. The cross guard has a hollow center, and a sharp diamond shape with pointed edges that matches its pommel. The rain guard is adorned with jewels, that emenate with regality.

History
Excalibur suddenly fell from the sky and was stuck in a huge rock in the Kingdom of Camelot, where people believed that it was a holy sword of God. Many Holy Knights tried to get it out, however, they failed until the appearance of Arthur, who successfully pulled out the sword, and became the new king of Camelot.

Current arc
After Camelot was taken by the Demon Clan and placed under the control of Zeldris of the Ten Commandments, the demon tried unsuccessfully to remove the sword from the ground where it was stuck.

Some time later, Arthur decides to infiltrate the castle to retrieve the sword and use it in battle against the demons. After seeing wounded Cath, and a conversation with Meliodas, who betrayed his friends, an angry Arthur pulls out the Excalibur.

Merlin explains that Excalibur in the past was just a common sword, given to Carfen, a master swordsman. While on the brink of death, he cleansed his sword with his blood and soul. Instead of becoming rusty, the sword became sharper and stronger as it had been infused with Carfen's essence. The blade's next wielder did the same, as did the next wielder of Excalibur. This process repeated countless times over millenia, each knight inheriting Carfen's will and cleansing the sword with their blood in the event of their death before passing it along to its next wielder. After a time, the sword began to choose its wielders, deciding if a person is worthy or not of wielding its might.

The kings of Excalibur chose Arthur. chapter 255 page 22

Abilities
Although many of it's abilities are unknown, Excalibur is a magic sword that won't bestow it's power upon anyone except the one it has chosen. The source of its power is neither from the Demon Clan or the Goddess Clan. It is a divine sword solely of the Humans, imbued with the souls of the master swordsmen who've wielded it in past millennia. Zeldris, Cusack and Meliodas all recognize the blind swordsman's sword style Arthur gained after he drew the sword, called The Dance of Avidya. Arthur was able to easily overwhelm Cusack, Chandler and Zeldris nearly simultaneously with Excalibur.