The situation of the Taiyin Hunyuan Ancestor was dire; he fed himself to the demon, offering a sacrifice to the Demon Sword, uniting human and demon. Had his mana not been profound, he would have been sucked into the sword along with his flesh and Primordial Spirit long ago!
The power of the Heavenly Demon Immortal Slaying Sword itself was extraordinary, but still limited. What truly made it formidable was the might unleashed by burning life essence in the Human-Demon Union.
Shi Feiyang estimated that if he offered himself as a sacrifice, first achieving Human-Demon Union with the Nine Child Mother Sky Demon, and then Human Sword Unity with the Nine Immortal Swords, he should be able to slay Venerable You Tan.
However, in that case, it would no longer be a human controlling the demon, but the demon controlling the human.
