Xin Chenzi had used the Bloody Soul Refining Technique of the Green Robe Ancestor, grinding a person's physical body into a pool of blood and flesh. Once the person was killed, their soul couldn't escape either, being bound entirely by evil skill and mixed with the tattered flesh. Then, by infusing his own mana and essence energy, he refined it into a stream of blood energy to wield the most malevolent secret techniques.
In the original text, the Green Robe Ancestor could use this method to temporarily entangle the Heavenly Demon Blood Transformation Divine Saber.
Xin Chenzi had directly killed ten of the Red-haired Ancestor's disciples, transforming them into ten streams of blood energy.
