Hitsuji no Uta

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)Abandoned by his parents at the age of three, Takashiro Kazuna was sent live with relatives and has grown up in the care of his aunt and uncle. Now in high school, Kazuna begins having reoccuring dreams of blood and death. Not knowing where to turn, he returns home to his parent's house to find Chizuna, his younger sister living alone in the big empty house. He learns from his sister that his father committed suicide some six months earlier, a fact that was intentionally hidden from him. When Chizuna learns about his dreams, she explains that he is suffering from the Takashiro family disease - a curse which causes an uncontrollable craving for blood - a curse that has already taken the lives of his parents and that Chizuna has been suffering from since childhood - a curse that is now beginning to effect him.