As an incarnate you are the bodily incarnation of some archetypical heroic concept. You have a basic concept that can be described in a few words. This is often an elemental association; fire, air or electric powers. Other examples include illusionism, telepathy, telekinesis, or regeneration. Yet others emulate legendary creatures like faeries or werewolves.
All Super powers should run in this theme. If your attributes and non-super powers are thus limited too, it counts as two limitations.
This is pretty strict; in City of Heroes an example would be a fire/fire blaster with a well motivated travel power.