From Shoujo Crusade:

A succubus is a demon who feeds on men's life energy. Richille, a fallen succubus who lacks sensuality and magical powers is sent to the human world to learn about seduction. There she meets Yui, a human who hates demons. Richille who wants Yui decides to make him the target of her seduction...!? But in the midst of that, something unprecedented happens...!?