Nial was not ready to give Khain a chance to excuse himself for losing against him. Thus, he didn't feel like using a runic armament to evade the high-velocity punch that almost reached him.
Nial knew that Khain was using a different martial art technique than before but he had also concluded that one of the Valxian's abilities was to create a second impact with the mana he released from his body.
Thus, the moment Khain hit something, a second impact would be created, causing more damage than the first one.
This was something Nial had to avoid until he knew if the second impact had a penetrative trait or not.
He didn't plan to get defeated because of a stupid mistake and it was because of this reason that Nial twisted his body in an uncomfortable angle to evade the high-velocity punch.