Legend has it...  in Chang'an City, there exists a hidden place, known as The Demon Hall ruled by the two Lords - the Cat Lord and the Snake Lord. Their movements are mysterious.  Apart from these two and their four deputies, no other demons are allowed to step into the human world to cause trouble.  This also helps them avoid their old nemesis.  Yes - that nemesis is Lord Changxi, the Celestial Master. He and the imperial court founded the Xuanjian Division, a bureau dedicated to investigating matters of demons and ghosts, and determined to wipe out all evil spirits. The two sides fought openly and in secret, until Lord Changxi, in the end, withered away and passed from the world.  From then on, the Demon Hall balanced the two realms, maintaining peace between humans and demons.  The Xuanjian Division became an empty shell, yet now - demon spirits pass through the land, with eerie shadows flickering and the storm will inevitably rise again. A word of advice - in this Chang'an city, it's best to go out after dawn...  and before midnight...  go home!

Hu Zhu is a fox spirit is one of two deputies of Cat Lord
Ling Xiao is a wisteria spirit is one of the two deputies of Snake Lord