I really enjoyed this series. It is one of the few I have actually watched twice.
The thing about this series is that it is almost more interesting as a survey of the Japanese Occult than for the story itself.
The story is about Kohei Morioka who is a photographer for hire. He investigates a castle in Germany but while there, becomes ensnared with Hazuki, a young vampiress. She bites him and tries to make Kohei her slave, but something goes wrong with her magic and she cannot control him, a fact that enfuriates her. In fact, he takes pity on her and tries to help her, unaware of the bigger mysteries behind how she came to be a vampire.
It takes time to develop a liking for the two main characters - Kohei and Hazuki. Kohei is way too over-patient with his impetuous and willful charge Hazuki, and Hazuki is a pretty selfish girl. But as the two adventure together, slowly a connection is made which becomes key in the final episodes. It is cute and humorous, and an enjoyable watch, but not necessarily the best there is in this genre of anime. Definitely an enjoyable watch though.