Didn't the duel end on a draw? Why is Shion saying that she lost?
Some readers were saying that the blade edges tell a different story: Shion had just made a shallow shoulder cut, while Frost was positioned to cut Shion's throat out.
I don't think so... As someone who trained with katanas and other blades, a descending cut on the shoulder like that has a massive chance of being fatal. That's where the subclavian artery is. If that is cut, you'll bleed out very quickly.
Also, for me, it seemed like Frost's attack would hit Shion's mask. And since that IS a "supernatural" element, we can't know for sure it'll be able to tank the attack or not.
So, for me it was a draw.