No one can step into this underground castle, no one can come out of the castle alive, no one can escape the death warrant issued from the castle, and no one can tell what kind of horror is hidden in the castle. That is truly an area where even gods and Buddhas cannot approach. The bloody smell of death is everywhere. Thousands of black crows gather all day long, their strange eyes shining with a cold red light, which is strange and terrifying. Those are messengers raised by the owner of the castle - purgatory birds. He is specifically responsible for delivering letters from the castle master to the leaders of various branches around the world, and reporting on the monthly status and results of each branch. The purgatory bird is the true messenger of hell. And that castle deep underground is the secret night killer group that makes people in the world and even court officials frightened - the World-Destroying Dragon King. They go against the will of heaven and serve the God of Death. The holy dragon is the king and the dragon walks the world.