Happiness 4 by Shuzo Oshimi

Makoto begs Nora to undo the horrific change she has wrought upon his body, even as Yuuki is increasingly consumed by his own thirst. Unaware of his escalating taste for violence, Yuuki’s girlfriend Nao is convinced that her affection can tame the beast he is becoming. But even if the love of a girl will be enough to stop the body count from rising, Makoto is coming to realize that he’s merely the newest player in a very old war…