Then, in the shop press the Power Aura and choose Equip. Load up any level and either press Square or touch the Power Aura symbol in the top left corner of the screen, then press use. This removes all enemies from the current level. The trophy will unlock when you finish the level.
This didn't unlock for me on my first try, possible because I had walked right for a few seconds first, so to be safe use it at the very start of the level before moving.