The dark art of summoning spirits.

"Sir, I heard that you were looking to practice the art of controlling spirits. As you know, The first two parts of the cultivation manual are inherited directly into the body and mind so there is no official written record. There was once a time when many people had made and sold fake copies of this cultivation manual but the demon king has put a ban on their production and distribution so you would no longer be able to find those fake manuals. Even if you managed to find one, it would be completely useless to you." 

Hua Tianshu's eyes narrowed down on the demon who was trying to advise him. 

"Are you telling me that just because the demon king banned it, nobody sells it anymore?"