Cultivators capable of becoming Nascent Soul Ancestors, each and every one of them, are not ordinary individuals, having emerged from mountains of corpses and seas of blood. Not even in death would they accept a contract that allowed them to be controlled by others.
However, Venerable Huijing was an exception to this, as he had been influenced by "Telepathy" to plant subconscious suggestions and was like a blank sheet of paper.
In reality, it required the arrangement of a specific Formation, something that posed no difficulty for Li Shiming, an Array Master. The type of Formation needed for the inverse unequal servant contract could be easily arranged by him.
The last, and most crucial, requirement was that when a Nascent Soul Ancestor signed the contract, their spiritual power couldn't be overly strong.
One certainly couldn't have a Nascent Soul Ancestor unleash their power on oneself, resulting in severe damage to one's own spirit.
