Excalibur

Excalibur
Excalibur is currently the rarest sword in game, as it was only obtainable during a limited time event in February 2017. Only 3 players are known to have obtained this legendary sword, DarknessHorseman (who owns 2 for being Support Team), Sonickfreek8, and Whitesamurott. Not only is this weapon incredibly rare, it is also incredibly powerful, trumping all other weapons currently in game by a significant margin, even while accounting for dual wielding weapons. It is currently unknown if any other events similar to the Excalibur event will be released in the future, but it is very likely at some point. The Excalibur sword is likely based off of the one used in the anime, Sword Art Online, but may just be in reference to the Arthurian stories about the Knights of the Roundtable.