You announce the value of X and how the damage will be divided as part of casting Aurelia’s Fury. Each chosen target must receive at least 1 damage.

If Aurelia’s Fury has multiple targets, and some but not all of them are illegal targets when Aurelia’s Fury resolves, Aurelia’s Fury will still deal damage to the remaining legal targets according to the original damage division.

If all of the targets are illegal when Aurelia’s Fury tries to resolve, it won’t resolve and none of its effects will happen. Nothing will be dealt damage.