Devil King

Every premise in KonoSuba runs back to one figure. The Devil King is the monarch of the devilkind, and his army of monsters wages open war against humanity, pressing hardest on the Kingdom of Belzerg, whose borders touch his territory. He rules from a black castle wrapped in a powerful barrier, with eight Generals ranked at the top of his forces. His threat is the engine of the setting's whole economy of souls: the gods offer the dead of other worlds reincarnation, cheat gifts included, precisely to raise champions who might slay him, and the reward posted for the Devil King's defeat is vast enough to anchor every adventurer's daydream. The king himself stays behind his barrier, a distant final boss whose face the beginner towns of the world have never needed to fear up close.