Ren would disappear into mists right as the blade would've connected, it would all seem like blur to nexus, as the darkness enveloped him...
An unnatural voice, not that of the boy he fought would eminate through the smoke, "Your Weak, pathetic, child's play" 

Ren's greatsword would then come swinging out from the shadows as they recede a split second after he disappeared, the blade thrusting toward Nexus's spinal column, the blade completely shrouded with shadows that almost whisper the lamentations of the damned. Ren would attempt to grab the man as he thrusts the blade forward with his dagger, pushing him into the strike and whispering "I taste the essence of your very soul.... it is sweet..."