Heaven's Secrets Technique.

Previously, the Heaven's Secrets Elder had mentioned that once you cultivate it, you are essentially cut off from the imperial throne.

At that time, Li Qinghai felt that the Heaven's Secrets Technique had significant side effects.

Therefore, when he initially wanted Hou Huanxi to cultivate it, Li Qinghai personally read through it carefully to check if there were any other unknown side effects.