Satan created 72 children immortal and immune to any injury, unless inflicted by a weapon forged in the fires in hell. Each child was given a weapon and told to fight for their survival. The sole winner will become the new king of hell. Hagino Sin, the child despised most by Satan, escaped the netherworld and tricked a kind-hearted writer into taking him home. The plan backfires and Sin becomes attached to the his savior and his friends at school. Sin must fight for his survival and kill his siblings before they kill him. Can he survive without losing his newfound humanity?