Haiji is Hazuki's guardian spirit. Haiji originally belonged to Kouhei's mother Chizuru, but she lost most of her memories of her when she was reassigned to Hazuki.

(Source: Wikipedia)

Morioka Kouhei wants to become a photographer. Unfortunately, he has the tendency to unintentionally capture the images of ghosts on film. 
One day, he visits an old castle in Germany where he meets a vampire girl, Hazuki. It turns out that Hazuki is confined in the castle against her will. She tries to turn Kouhei into her slave by sucking his blood, with the intent to have him break the device sealing her in the castle. Although Kouhei proves to be immune to the vampire's curse, he is eventually forced to help her. Hazuki successfully escapes from the castle and leaves for Japan to look for her mother. 
When she arrives in Japan, she goes to Kohei's house where he lives with his grandfather, who agrees to take in the girl. Due to his own childhood experiences, the sympathetic Kouhei agrees to aid Hazuki in her quest. 
However, other vampires, including Elfried and Count Kinkell, manage to track Hazuki to Japan. They will stop at nothing to retrieve her. 
(Source: AnimeNfo)

Masami Yamazaki is a Japanese voice actress best known for her appearances in Immortal Grand Prix, Moon Phase, and Pani Poni Dash!

When you come from a family of exorcists and mediums, you're expected to have certain powers. But despite having a psychic lineage, Kouhei Midou can't predict the future, nor can he see dead people. He's powerless in every sense of the word. However, he does think fast on his feet--and with a little help from his psychic cousin Seiji, he's an amazing crime solver. 
The mystery he wants to solve more than anything is his mother's tragic disappearance. But it isn't easy ... especially in this world, where nothing is as it seems. Cats talk, blood-sucking vampires roam the earth, and monsters eat guys like Kouhei for breakfast. Can Kouhei survive this chaos long enough to find the mother that he's lost?! 
(Source: Tokyopop)

Omake Special from the final DVD volume. The Special storyline has very little to do with the original series outside of having some of the same characters, and has a completely different storyline which does not fit into anything which came before it.