The world is full of them.
they crawl in the earth and fly through the air. they swim in the waters and run wild in the fields. they lounge in the cities and climb in the mountains and fairly burst from the caves and pockets in the surface of the world.
they are all around us, even as we speak.
and they are all completely invisible.
they usually leave we humans well enough alone. most of them are completely harmless. most of them. once in a while though, statistics say one will inevitably be born with power. real power. and if that power is ever discovered, you could guess what would happen next.