It just occurred to me as I was browsing some TE art and TSFiA books...
Spoiler for For the last known LN chapter. Don't say I didn't warn you:
So, Yui was shot via a sniper rifle, and left to drown in her own blood, right?
Now, take a good, hard, long look at nearly half of all Cryska pictures, and cover of TSFiA volume 2. What is Cryska carrying?
That's Dragunov, the Soviet's marksmen weapon of choice. Now, we don't see Cryska doing any shooting as an infantry trooper at any point is story; why would she ever have to wield the gun?
Now, think again.
Yui is sniped. The only character we have remotely seen holding a sniper rifle? Cryska.
The chilling part is that this is totally in-line with what Sandek might be planning; and would be something that Kouki would love.