@SaintRavenmane
Aura said that Frieren is using anti magic to dispel her spell, and that it must be consuming much more mana than just blasting the undead army away. She doesn't understand why Frieren doesn't do the latter and conserve her mana as it is illogical. Frieren then answered that Himmel had gotten mad at her for blasting the undead army away as she had done, and Aura responds that since Himmel is gone, she shouldn't have to worry about that anymore. I'll be honest, whatever Himmel's reason for getting angry was, it is incredibly stupid to be wasting your energy in a life and death situation. If Himmel was around in our world, he would get angry at our armies for wielding explosive devices that desecrate the body of enemy soldiers by disintegrating them. And to be fair, there are always limits - we've banned chemical warfare and nuclear devices are used as deterrent - but it seems unreasonable to ban blasting an army of undead.
It's really interesting to see these interactions, because it shows that these demons are genuinely curious creatures (which makes sense, as they take pride in their pursuit of magic) and very logical. They simply lack empathy and also feed on humans. This exchange also shows that even after the disappearance of her comrades, Frieren was changed by the bonds she had made and the time spent with her companions. A demon on the other hand would not have changed. Their nature would have remained the same and if anything that impeded on it disappeared, they would revert to what they are.