This anime about the relationship between Kouhei Morioka a freelace photgrapher and Hazuki, a teenager who descends from a royal vampire lineage.
We learn at the start of the story that Kouhei travels to a castle in Germany to take photographs of all sorted Paranormal phenomenon for his friend Hiromi, the editor of an occult magazine. At the castle, Kouhei meets Hazuki, who feeds on Kouhei's blood and claims him as her unwilling servant. She is a 14 years old vampire - selfish but adorable - who was separated from her mother and restrained in a castle in Germany.
Although this "blood pact" is supposed to bind Kouhei to Hazuki as her obedient slave, her act has no effect on Kouhei. Following an action packed sorcerers battle, in which Kouhei and his cousin manage to free Hazuki from her captivity in the dreary castle, Hazuki travels to Tokyo, and takes up residence with Kouhei in his grandfather's house in Japan. Hazuki reveals this is what her mother wanted her to do when she disappeared.
Hazuki claims that, because she fed on his blood, Kouhei is now her servant, but Kouhei continually refuses to obey her, especially when he thinks her requests are unreasonable. Despite their fighting, the relationship between the duo progresses over time - even in the face of repeated attacks by opposing vampires - until Kouhei becomes determined to protect Hazuki from the vampire servants of her family, who themselves are determined to retrieve her by whatever means necessary.We learn later on in the anime he possesses great spiritual powers which were sealed by his family in order to allow him to live a normal life, as they were too strong for him to control. In the anime, he once again seals away his Jyougan so that it doesn't affect his relationship with Hazuki.
Other characters include Ryuuhei is Kouhei's grandfather who took in Hazuki and is a powerful spiritualist and exorcist.
A word about Revelation's DVD packaging. It is beautiful with pop up disc holders and a set of guide notes to further explain things as well as points to look for in later viewings.
Below is a picture of it in exploded form: