X-Blade

Spoiler Alert!

The X-Blade is a Keyblade Ventus uses while possessed by Vanitas in Kingdom Hearts: Birth By Sleep. It looks like two Kingdom Keys merged together, with a bit of filigree on each side like that of the Ultima Weapon. With the help of Mickey Mouse, Aqua defeated Ventus/Vanitas and destroyed the X-Blade, casting Ventus into a deep slumber from which he has not yet awoken from.