I wonder how you would resolve the following situation:

Slaanesh players use his rolled hits to destroy two upgraded Plaguebearers. Now Nurgle player has to assign hits from their upgrade to kill any unit(s) of Slaanesh (they do not stack with other types of hits). But there are only upgraded Deamonnettes in the area, and according to the upgrade card:

In battle, Daemonettes can only be hit by battle die results of 6.

How do you think, does this protect Daemonettes from such hits?

As I see it, the hits by the upgraded Plaguebearers are NOT hits from battle die, but from a special ability, so the Daemonettes special ability (which only counts when the enemy uses battle die to attack) does not activate in this case - so the Daemonettes will take the hits.