Purchase all of the Character upgrades in the game. In order to be able to purchase them all, you must complete all 180 of the challenges in the Web of Destiny. You then must have enough essence (currency to buy upgrades) to purchase them all. You can check/buy them in the main menu, or during the game itself by pressing and selecting it, or even by pressing and using and to cycle through. You will not have enough essence to upgrade both Character upgrades and Combat upgrades in one playthrough. You should however get enough money while going for plainum medals on hard mode.