Hitsuji no Uta

Kazuna's family carries a hereditary disease that causes an overwhelming, vampire-like hunger for blood. Unaware of this, Kazuna was raised by the Eda family as a child. When he starts showing symptoms of the illness, he meets his older sister, Chizuna, who has lived with the condition since she was young. Understanding the heavy toll the disease takes, Chizuna tries to support her brother and teach him how to manage his cravings-but the struggle is far from simple.