i really want to know why vanitas makes the x blade and what does it do??

The ?-Blade (?????, K?bur?do?) is a legendary Keyblade introduced in the Kingdom Hearts prequel, Kingdom Hearts Birth by Sleep. According to Master Xehanort's reports, the X-Blade was an alternative method to opening Kingdom Hearts. As written in Report 7, he stated that "unlike the Keyblade, which existed to join Kingdom Hearts, the X-Blade existed alongside Kingdom Hearts".[citation needed] Presumably, Master Xehanort believed that lust for the power gained from opening Kingdom Hearts and, thus, the urge to create the X-Blade to open Kingdom Hearts was the reason behind the Keyblade War.

 

Ventus was trained by Master Xehanort so that he may use it to open the door to Kingdom Hearts, creating Vanitas from the darkness in Ventus's heart to achieve this goal. The X-Blade was finally created when Vanitas fused with Ventus, though both their fusion and the ?-Blade were incomplete. Ventus fought off Vanitas (wielding the incomplete X-Blade) inside their Awakening while Aqua and Mickey Mouse fought off Vanitas/Ventus (who wielded a completed X-Blade) in the Keyblade Graveyard. Thanks to the combined efforts of Ventus, Aqua and Mickey, the ?-Blade was destroyed along with its wielder, Vanitas.

 

Within Xehanort Report, he stated that the X-Blade could be created when a heart of pure light and a heart of pure darkness intersected, both of their powers being equal. With the creation of the X-Blade, Kingdom Hearts, being the heart of all worlds, would form and one would be able to use the X-Blade to open Kingdom Hearts. As a result, Master Xehanort used Ventus as a tool to create the X-Blade as he split his heart into one of pure light (Ventus) and one of pure darkness (Vanitas).

^I read every word you posted on something else.