Lament of the lamb - Kei Toume

Kazuna, a teenager whose past is shrouded in mystery, continues to struggle with his strange new disease - a violent and irrepressible craving for blood. His violent attacks draw him closer to Chizuna, his long-estranged sister, who suffers from the same scourge, one that has ravaged their family for generations. As Chizuna reveals to Kazuna the secrets of his past, she finds herself connected to him intimately as their destinies intertwine. This complicates her relationship with Minase, her young doctor long in love with her. Kazuna and Chizuna are each other's best hope and reason for survival, enough such that he leaves his home, so the two can forever be together. The struggle rages within Yaegashi, Kazuna's girlfriend, as well as she tries to come to grips with his terrifying illness, Kazuna's sudden alienation from her and how, in the midst of this confusion, she can bring herself to express to the boy how much she really loves him.