Peterene Sera is a priestess to the Goddess of Chaos.
When she was little, a Demon God killed her parents. Louie's father Guraza took her under his protection, and by the time Louie begins his war against humanity, she is working as one of his servants.
Initially Peterene wears a heavy cloak with a hood concealing her face. Everyone believes this to be a way of concealing burn scars that disfigured her when she was younger; it's actually meant to conceal the fact that she's a human, and was Guraza's idea in the first place. By the time Louie discovers this, his own opinion of humanity has begun to soften, and Peterene is able to serve openly and without fear for the remainder of the series.