Go to the world that never was and go to the proof of existence turn into the forms as you walk into one of the two doors kill as much as you can before your Drive runs out. And all of you have to do is go back to the save point to jump back to the world and can go back to the proof of existence and repeat just make sure you are in your form when you go to the world and your form will be full when you come back. However this only works on these forms for valor and final and if you didn't know wisdom form and master form required different stuff that cannot be obtained in the world that never was. For the people that don't know master form you need to collect orbs and wisdom form you need to kill heartless