This is what Chen Fei found when he had slain Zhang Chaoyun and extracted the essence of spirit. At that time, Chen Fei had only been thinking about extracting the essence of spirit; as for the essence of soul, he hadn't harbored high expectations.
Unexpectedly, in the end, he had managed to extract the essence of soul along with it, although it had been somewhat difficult, he had achieved it.
Afterward, Chen Fei had even tried to eliminate the traces of his own soul left in the void, which had also been possible, just like when he had been in the Combined Aperture Tempering realm.
While other techniques had needed to be reintegrated with the techniques of the Mountain Sea Realm, only this residual form of the Slaughter Spirit Technique had not required it. This had made Chen Fei curious about the origin of this Slaughter Spirit Technique.