x-blade

The χ-blade is a legendary weapon introduced in Kingdom Hearts Birth by Sleep. It is the original after which all Keyblades are imperfectly modeled from. Rather than being a man-made key to an artificial Kingdom Hearts, like the Keyblade of heart, it coexists with the true Kingdom Hearts itself, a perfect union of all hearts and worlds, and is the only thing that can summon its door. According to legend, the Keyblade War occurred because of the many souls who desired to take the χ-blade and Kingdom Hearts for themselves, and Master Xehanort later enacts his plots with the same goal in mind.