Once upon a time, in this vast world, the door to the underworld was opened, and countless demons and monsters poured into the world.
Since then, there have been traces of demons in the human world. It's just that the existence of the demon exterminator prevents some evil demons from causing harm to the world. Otherwise, what will happen if the order in the world is in chaos?
It's just that no one cares about the demon in the dark, the tears and loneliness behind them.