The voice of a child coming from within the cauldron was actually the Heaventide Holy Beast's incarnation that Han Li had captured during his battle with the Endless Sky Saintess.
This beast, originally a demon beast that acted on instinct, had, after being trapped in the Heavenvoid Cauldron for over a hundred years, spontaneously awakened its spiritual intelligence, even regaining most of its memories from the spirit realm. However, being confined within the Spiritual Treasure of the Heavenvoid Cauldron, the beast had no escape and could only stay put obediently.
After Han Li advanced to the Deity Transformation stage in the Star Palace, he immediately re-cultivated the two heavenly skill spirit treasures.
As a result, after completing the cultivation of the second level of the Treasure Commanding Decree of Heavenvoid Cauldron, he was finally able to open the cauldron.
