Salaryman-turned-heavenly king Uchimura leads the Demon Army against a horde of invading wyverns. The army struggles valiantly but is overwhelmed by the appearance of a titanic dragon--that is, until the Demon Overlord arrives. After dealing with this threat, the Demon Overlord makes the following unexpected announcement: "You, Uchimura, shall become the next king of the Demon Army!!" While striving to deal with this unexpected promotion, Uchimura heads to his next mission, where he faces a new, severe problem.