In 2012, a man-made virus decimates the global population, sparing only children. Soon, vampires emerge to fill the void, assuming control as supernatural horrors of legend spread across the earth. The vampire overlords force the remnants of humanity beneath the surface, promising safety in exchange for donations of blood. Trapped in an underground orphanage, young Yuichiro Hyakuya plots to break free with the rest of the children. When their escape attempt is thwarted, Yuichiro vows to avenge the deaths of his fellow orphans by terminating vampires.