A Storm is Brewing

Primordial Spirit Guide was devised by Qin Mu and Ling Yuxiu by combining the theory of the most basic technique of Overlord Body Three Elixir Body. Its basis rested in Daoyin Technique who was used to guide the vital qi.

Meanwhile, Primordial Spirit Guide guided one's spirit embryo to mix with another person's soul before flying out of their bodies. The soul and spirit would then swap back, taking the chance to merge into primordial spirit.

Therefore, the technique needed to have a 'guide' word in its name.

The reason why Qin Mu's primordial spirit could resonate with Si Yunxiang's primordial spirit was because of his spirit embryo. It had no attributes, which was unlike the spirit bodies of Si Yunxiang and Ling Yuxiu who had their own attributes.