Kakyu, a former Japanese who was reincarnated as a low-level demon in hell, has acquired unparalleled strength over two thousand years. However, unexpectedly, he is exiled to another “different world,” liberated from the harsh underworld. Kakyu, who was enjoying his dream slow life, witnesses the village he owes everything to being attacked. Despite rushing to the scene, the village is annihilated. Picking up the only surviving baby, Ars, Kakyu resolves to raise Ars to become the happiest person in the world to repay the debt…!?