User blog comment:Hidden Scorpius XI/My impressions on Volume 4, Chapter 6 (Tipping Point)/@comment-4010415-20161212044413/@comment-25936766-20161214002805

"The slow-motion was used to signify the point Ruby's Aura hit the zero mark."

....Or, just to show that it was quite a strong hit, dealing much damage. Not necesarily reducing her Aura to 0, especially since then she should've been more....unconscious.

Besides, Tyrian was about to stab her, and if she had no Aura left that stab would've killed her, which goes against the orders Tyrian's beloved Goddess gave him.