Mana in its pure form was present everywhere, and whenever things moved, they displaced its position.
This was a simple observation made by Luan when he just started using man in Thorn Forest.
As someone who was filled to the brim with nothing but pure mana, these displacements we're as clear to Luan as the sun to anyone.
He had tried to figure out how this might help him in his day to day life, and he discovered that of he focused on the mana in the atmosphere itself, he could sense the displacements, and although it wasn't clear, it was enough to give him an edge over sneaky opponents, human or not.
After gaining this ability, Luan hadn't really put much thought into it because he was satisfied by its usefulness, but his thoughts changed in this fight.
The moment before the sword grazed his shoulder, he "saw" the mana ripple slightly and extend forward towards his chest a second before the sword hit.
