Χ-blade

The χ-blade is the legendary Keyblade that is the counterpart to Kingdom Hearts. When Kingdom Hearts was lost in the deepest of darkness, the  χ-blade was shattered into 20 pieces. 7 of light, and 13 of darkness. Tales tell of a Keyblade War, where countless Keyblade wielders created their own Keyblades to the image of the  χ-blade. They fought each other and desired to take the  χ-blade and Kingdom Hearts. Master Xehanort's goal is to aquire the  χ-blade and start another Keyblade War. He first attempted to create it by having a heart of pure light (Ventus) and a heart of pure darkness (Vanitas) clash together. Vanitas managed to fuse with Ventus, and the   χ-blade was created. During a metaphysical battle, the   χ-blade was still incomplete and Vantias attempted to complete the fusion within their combined hearts, but Ventus sacrificed himself to stop Vanitas. During a physical battle against Ventus-Vanitas, Aqua and King Mickey managed to destroy the   χ-blade, 'causing it to explode.

Trivia

 * In the Jeffrey, Jaden & Friends' Storm Adventures series, the  χ-blade was broken into 11 pieces of light. Not 7.