Chrno Crusade

Chrno Crusade is one of my favorite anime. This Fictional tragic story is about a nun (Rosette) and a demon (chrno) happend in 1920.Both Rosette and Chrono are revealed during the course of the story to be driven by a shadowy past, centered around a search for Rosette's lost brother, Joshua.

If you are interested about the story, you can read it at http://onemanga.com

I don't know where to find the anime video series, try crunchyroll or just google it .^^