Intelligence
Furthermore, there was no point in trying to kill each other now.
The battle was over. The core reasons for their bloodlust; the desire to break through, had also gone.
If anything, Rui valued him. He was probably the one man who would never be anything less than extremely difficult for Rui to defeat, no matter how many times they fought.
Rui's Martial Art was such that once he fought someone, they would never be able to defeat him ever again under ordinary circumstances. This happened with Kane, who lost to him even on a battlefield where he essentially had limitless stamina for a powerful grade-ten technique fueled by the environment around them. Not even such overwhelming situational advantages could allow Kane to defeat Rui.
The VOID algorithm when adapted was too powerful, and it never forgot.