Clarent

History
Clarent was a sword built by all the knights of the Round Table as a sword of peace, meant to be used once they controlled all of Europe.

Power
While it is meant to be a magical sword used in times of peace only to destroy weapons, this can be abused by evil to destroy swords of good, as shown in Mordred and Arthur's battle.

The Sword is designed as an anti-sword, being able to destroy any magical sword, regardless of strength. However, the condition to this is that if Clarent is ever used as a sword against flesh, it will be destroyed itself, and the other swords will reappear in the place they were built. This is used by Ten Beard in order to obtain Excalibur.

Wielders
While all of the knights of the Round Table were destined to wield it at some point, and each got to test it out against normal broadswords, Mordred and Agravain are the only ones to have used this in combat, with Ten Beard only using it as such to intentionally break it.