C1598

The disciples' words immediately reminded Li Xiaobai. Other than the various Empyreans and almighty beings, the most powerful soul summoning technique in the Pangu's Realm was definitely the Underworld, so to learn it, one had to go to the Underworld. However, this was the Supreme Purity Sky, and was very far away from the Underworld.

Since this was the Great Wall of the Heavens