Hitsuji no uta (2003) IMDb
Kazuna learns that his sister is afflicted by a very painful disease, half-jokingly referred to as vampirism. Their parents are already gone, and the affliction starts to manifest itself in the boy, placing his high-school friends in some peril. There are no advantages. Even the compulsive hematophagy does not save anyone in the long run.
Tragic horror. A more serious Haibane Renmei (2002) in some respects. Certainly a neat sublimation of pubertal insecurities with incestuous urges. Little animation (lots of repetition) and some monomaniacal direction: Frequent non sequitur trains and (de)saturating transitions. Some odd design choices: unusually thick nose lines, box eyes with thick details and skin-toned glasses. The title means “Song of the Sheep” or less directly, “Lament of the Lamb”.