Unique Ea

"Though it is wielded by Gilgamesh, who has the prototypes of every Noble Phantasm, the Sword of Rupture Ea is different from the other Noble Phantasms that can be possessed by other heroes. It alone is a completely unique existence that can only be possessed by Gilgamesh. Therefore, even with Unlimited Blade Works, it is impossible to reproduce it."

Fate/Zero Anime Visual Guide II