Mu Yunxi and Liu Qingqiu were both cultivators from the High-Level Cultivation Realm, and they had both seen Heavenly Demons and even participated in their encirclement and suppression.
Some sects in the Cultivation World would use Heavenly Demons as trial objects to lessen the fear disciples would face when they encountered such demons.
Only by overcoming the fear of Heavenly Demons in their hearts could they avoid providing the very fear that Heavenly Demons needed to become stronger during a confrontation.
When some Heavenly Demons encountered cultivators, their strength often was not as formidable as that of the cultivators; however, should a cultivator be so frightened by the sight of a Heavenly Demon that they were paralyzed with fear, and considering that Heavenly Demons could magnify the fears in one's heart and feed off the power generated by that fear, it was common for a Heavenly Demon to become more powerful than the cultivator it faced in a short time.