The so-called emperor-level cultivation arts were secret arts created by those ancient kings and sovereigns, and were not handed down to posterity. Among them, some were a complete cultivation technique set, while some were secret techniques.
However, no matter which, their might was extremely astonishing.
Their mysteries and strengths were inconceivable and were naturally incomparably precious.
In addition, emperor-level cultivators were rare, so they became one of the foundational resources of all forces.
However, most of them were basically unable to be cultivated because of the harsh requirements. For example, many of them needed to be combined with the bloodline power of the inheritance. This made almost everyone unable to fulfill the requirement.
Moreover, it was very difficult for other races to cultivate the emperor-level cultivation arts of other species, making it even harder to find a successor.