Since modern times, it has become a consensus that the three realms are not interoperable. Violators will be punished, and every city has enforcers who maintain the balance in the middle. They are gods, demons, or ghosts, with the exception of Yuncheng. Since a thousand years ago, the enforcers have been human beings. Generation after generation, they have always died in the search. This is their fate, a fate planted by themselves.
Purpose: People don't know monsters, and monsters cannot cross the line.