-Clear stage without a Villager fleeing.
Much like Episode of 2 for this Chapter the Villagers appear from the beginning of the fight and stay near the top of the map where the battle starts.
Once again this comes down to being proactive about clearing out enemies, especially big mobs with Captains and watching for the "Attempting to Flee" message.
As long as you keep an eye on the action going on up top and come back to help them clear out when reinforcements drop in you shouldn't have much trouble here.