The primordial source force of creation is the origin of the vast majority of power in this world, though its limit is the ninth grade. The so-called taboo refers to transcending the ninth-grade limit, mastering tenth-grade power, breaking through the limit of the source force, and thereby remaining unaffected by the cultivation system of this world.
The Divine Kings were the first batch of taboos, existences not to be offended, with invincible divine power.
Later, clever cultivators discovered that single-mindedly cultivating the source force alone could not make one a taboo, but if multiple limit source forces were fused—much like concocting pills or taming fire—there was hope of achieving a breakthrough. Immortal Kings came about in this very manner.
Chapter 2045