Ishura unfolds in a world thrown off balance after the demon king's death, when the vacuum he leaves behind draws self-proclaimed demon kings from across other worlds to the New Principality of Lithia. There, a brutal contest begins for the throne that could decide the future of the realm. Among the contenders is Soujirou Yagyuu, a master swordsman who wants the coveted title for himself, and he is joined by Tooi Kagizume no Yuno, the young girl he saved after an army of golems destroyed her city.
At the same time, Lithia becomes a target in a wider political struggle. The leaders of the Aureatia Kingdom try to destabilize the principality by sending bandits against the convoys carrying merchandise through its territory. In response, Imashime of Taren, Lithia's founder and a defector from Aureatia, dispatches the vicious thief Kasasagi no Dakai to uncover who is behind the attacks. As war edges closer, the rival claimants to the demon king's throne shape a conflict no one can fully predict.
