In essence, whether one follows the Daoist or Buddhist path, reaching a certain level of cultivation allows them to form their own core. From body refining and Qi cultivation to establishing a foundation and forming the Golden Core, every stage was meticulously documented.
Most of these books were tattered and damaged, likely collected over many years by Chong Jiu's master. After all, since the closure of the Celestial Gate a millennium ago, there had been no true cultivators in the mortal realm. Over the course of history, texts on cultivation methods had become exceedingly rare—so rare that not even the royal library of Mu Nation had more than a couple of such books.
Given that Chong Jiu's master could craft such powerful talismans, it was clear that he had made significant progress in his own cultivation.