Xuanyang Cave in Shanhaiguan is a "rift in time and space" - where the obsessions of gatekeepers, refugees, and soldiers from past generations converge to form the "Guan Soul". Lu Yuan accidentally fell into a cave and gained the ability to talk to the undead in history. He was forced to accept three "ghost apprentices" from different eras to help them fulfill their unfulfilled wishes, and finally revealed the secret of Xuanyang Cave that has lasted for thousands of years.
