Synch Blade is an ability which allows a Keyblade wielder to use two Keyblades at once during battle. It is unknown if in the Kingdom Hearts series, there are any characters that are able to equip this ability. So far, only Roxas is able to use this ability to summon his two Keyblades naturally, the Oblivion and the Oathkeeper in battle, and Sora while in Valor Form, Master Form, and Final Form.
Sora appears to be able to use Synch Blade during the final battle with Xemnas without using any drives.