After the demise of the demon king, the resulting power vacuum has broken the balance of the world. Eager to claim this power for themselves, self-proclaimed demon kings from various worlds assemble in the New Principality of Lithia to fight for it. Among them, master swordsman Soujirou Yagyuu seeks to take this coveted position for himself. Joined by Tooi Kagizume no Yuno, a young girl he saved from an army of golems that destroyed her city, Soujirou enters Lithia to battle his way to the title.

At the same time, the leaders of the Aureatia Kingdom seek to destabilize Lithia by launching bandits after the convoys of merchandise transiting through the principality. Enraged, Imashime of Taren, the founder of Lithia and defector from Aureatia, sends 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.