The foundation of Su Chengyu's strike with this sword lies in the Heavenly Fox Orb. After Bai Huang inherited the legacy of the Qingqiu Fox Clan, the Heavenly Fox Orb itself underwent a series of transformations.
Perhaps it's because the legacy of Qingqiu is no longer present, and what's left in the Heavenly Fox Orb is the pure essence of the Hongmeng Heavenly Book, still cloaked in the veneer left by generations of Qingqiu predecessors.
Now, the person controlling this veneer is none other than the Green Hillock Empress, who has a profound connection with Su Chengyu. Thus, Su Chengyu is confident that he can comprehend the Hongmeng Heavenly Book on the Heavenly Fox Orb.
