Following the death of the demon king, the resulting power vacuum has shattered the world's balance. Eager to seize this power for themselves, self-proclaimed demon kings from various worlds gather in the New Principality of Lithia to fight for it. Among them, master swordsman Soujirou Yagyuu aims to claim this coveted position for himself. Accompanied by Tooi Kagizume no Yuno, a young girl he rescued from an army of golems that destroyed her city, Soujirou enters Lithia to battle his way to the title. Meanwhile, the leaders of the Aureatia Kingdom attempt to destabilize Lithia by sending bandits after convoys of merchandise transiting through the principality. Enraged, Imashime of Taren, the founder of Lithia and a defector from Aureatia, dispatches the vicious thief Kasasagi no Dakai to investigate the origin of these attacks. With war on the brink of eruption, no one can predict what influence the contenders for the demon king's throne will have on the coming conflict.