It's a long story. Even the demons don't know where they came from, and need to live amongst humans. But humans instinctually fear them. So, they used to kidnap humans to do their bidding, so they could live amongst people. The government got involved to integrate them into society.

There's a lot more to it than that, but that is the gist of it. They look like humans for the most part, but they have this… smoky ethereal form as well.

[He takes his next move. He's tying to end this game.] Then again, I'm only aware of their uses as spell components.