This trophy is for using each character in the game. If you're attempting to complete the gallery, you will use all of the characters except for 3. Kuro, Cole and Toro will have to be selected in Versus or online modes as you can't select them in Arcade. Using the characters in the Mission Mode/Trials doesn't count, either. You can check how many uses you have with each character in the "Character Data" menus if you don't earn the trophy when you think you should.