Shard of Icarael
The Shard of Icarael is a unique sword that is received as a reward for completing part 1 of the side quest "The Legend of the Three". There is also a small chance to receive it as a reward for searching Unspoiled Ruins after reaching Era II.
The metals within the blade and its crafting style are like nothing else on Auriga. The beauty and keenness of the weapon have led many to speculate wildly on its true origin.