This is the Summoning of Spirits, allowing the summoning of demons from hell. This summoning is somewhat similar to the summoning from Ye Mo's Five Elements Door.
However, Ye Mo's Five Elements Summoning is an Original Summoning, while Yuwen Ke's is a flute-based summoning, far less powerful than Ye Mo's Five Elements Door.
But after Ye Mo's Five-Elements Cultivation evolved, he could no longer use the Five Elements Door, because his Transcendence Golden Body no longer existed, leaving only the Heavenly King Fojiang's Original Law Incarnation.
However, all those Five Elements Magic Treasures are retained. They are the materials he used to create the Butu Tower, and none can be spared.
As Yuwen Ke played, demons with wings, six arms, and giant horns surrounded Ye Mo and Gu Xingyue. Each demon was hideous yet extremely powerful.
All of them possessed Half-step Universe Realm strength, their attacks capable of tearing space apart and easily killing the Seven Star City Lord.
