Clair is a woman with a large sword who hunts down and kills demons. That’s basically the whole plot right there. She is part of an organization of forty women, each of which has to guard a certain region. These women are given enhanced abilities by having demon DNA put into them, which turns them into a powerful half woman and half demon. The reason men aren’t used is because they succumb too easily to the dark side of the demon form.
Clair is probably one of the strongest women in anime. Not only is she able to wield her large sword against large numbers of demons with incredibly efficiency, she is also able to reheal herself. Several times she has had body parts actually cut off of her only for her to reform her body parts. Clair will keep going to complete a mission and never give up, which makes her more successful than some of the other women in the group who have lower numbers than she does and are supposedly more powerful than she is. She even saves one of the leaders named Jean and Jean vows to work for Clair as her back up.