Believing herself to be a faithful priestess of a god called "the Absolute", this Child is named after the famous French martyr Jeanne d'Ac.
Someday, she may realize the fact that she's actually working for a demon now, but that day is not today. In the meantime, the misunderstanding on her part enables her to fight with a holy fervor that would be unthinkable for any other demon familiar.
One last nore: the being known as "the Absolute" that Jeanne's pactmaker so fervently believes in? It sounds like no one has ever actually heard of it...