Hyakki Yagyō

One night a group of demons patrolled through a significant part of Fiore. It is said that any one who got in the path of the demons were instantly killed by the demons. That group of demons is now known as Hyakki Yagyō (百鬼夜行, "Night Parade of One Hundred Demons") and the leader of this terrifying group is now known as Nurarihyon.