Zatiel's heart may have become a little less cold after the experiences he lived in the Deep Dark Dream, but when it comes to his enemies, he was still a ruthless killing machine that could kill billions of them without hesitation.
If his wrath was powerful enough or his bottom line was crossed, he could even ignore age and perform massacres of race extinction levels.
Hades showed nothing when he saw the Neo-Demon total disregard for the life of the people in this world. His ability to kill hundreds of thousands of people without blinking an eye did not come from his coldness, but from the fact, he had lived billions of years and saw countless generations perish.
A human would not feel bad for crushing an insect that was going to die in a couple of hours of natural causes, so why would a Beings of Laws hesitate at the moment of killing a group of people whose lifespan was no different than a nap for them?.
