Vampire-Princess Miyu is a series of 4 animated episodes originally released directly to video in Japan. In North America it has been released both subtitled and dubbed by AnimEigo. It is available at many video rental stores with a decent selection of Anime. The Vampire Miyu web page contains much more information.

Major Characters:

Himiko, a spiritualist:
She is basically a paranormal investigator who has encounters Miyu. She is the point-of-view charactor for the video series.
Shinma, Literally "God-Demons":
A class of supernatural beings. The proper place for these beings is the Dark. It is the job of the guardian to return stray Shinma back to the Dark.
Miyu, a Vampire-Princess:
Like most vampires she needs blood to live, but she has none of the other limitations, like sunlight and garlic. Normally Vampire-Princesses age and die, but Miyu's time has temporally been stopped, leaving her with a 13 year old body for the last several decades. Her mission, as the guardian, is to banish Shinma back to the Dark. Miyu is an elite Shinma.
Larva, a Shinma:
Miyu's only friend and slave. He always wears a mask and never speaks.