Even with Su Lin's current combat power being comparable to a Half-Emperor, combined with the exceptionally tough defense of the Resentful Dragon Sword, his use of the Word-Character Mantra, his ice armor, and Sanpin's tail wrapped around his body as an extra layer—even with so many layers of defense reinforcing him, Nangong Zhi's force still managed to seep through.
It was clear that without these defenses, that single palm strike alone would have stripped him of half his life, if it didn't kill him outright!
There was simply no way to fight this battle.
Chapter 581