The story takes place in a world where an unknown virus has killed the entire human population except for children under 13. Those children were then enslaved by vampires. The manga centers on Yuichiro Hyakuya, a human who dreams of becoming strong enough to kill all vampires. (Source: Anime News Network)The story takes place in a world where an unknown virus has killed the entire human population except for children under 13. Those children were then enslaved by vampires. The manga centers on Yuichiro Hyakuya, a human who dreams of becoming strong enough to kill all vampires. (Source: Anime News Network)