Hitsuji no Uta
Japanese title: 羊のうた
Alternative titles: Lament of the Lamb, Song Of Ram, Song of Sheep, Song of the Sheep, Sheep's Song
Type: OVA
Source: Manga
Episodes: 4
Status: Finished Airing
Aired: May 25, 2003 to Feb 25, 2004
Duration: 30 min per ep
Rating: R - 17+ (violence & profanity)
Studios: Madhouse
Producers: Group TAC, Ken Groove, Groove Corporation
Genres: Drama, Horror
Themes: Vampire
Demographics: Seinen

Kazuna's family has a history of suffering from a disease that creates an uncontrollable vampire-like thirst for blood. Knowing none of this, Kazuna was sent to live with the Eda couple as a child. As the sickness begins to show signs of being present within himself, he comes into contact with his older sister, Chizuna, who has been suffering from it since early childhood. Knowing that the sickness incurs a heavy weight upon those that suffer from it, Chizuna tries to ease her brother's burden, to help him learn to control his urges, but... 

(Source: ANN)