One of the martial arts Su Xin was most proficient in was finger techniques, and Zhongli Yan was also attacking Su Xin with a finger technique, not out of a deliberate challenge but because this particular technique itself was among the strongest martial arts of the Zhongli Family, known as the Heaven Opening Divine Finger.
This finger strike had no other intricate powers, only the most pure form of strength!
The alien tribes of the Northwestern Province all had their own martial arts heritage, and these ancient martial arts might seem somewhat rigid to modern martial artists, but in fact, the power displayed by any martial art when perfected is extremely terrifying.
Such is the case with the Zhongli Family's Heaven Opening Divine Mantra, which is purely about overpowering with strength.
