When Damien's body collapsed to the ground, he seemed to have gone through a myriad of changes. His hair became grey, his skin became wrinkled. He had aged hundreds of years in the span of a few seconds.
It wasn't just that his vitality was overdrawn or depleted. If that was enough to cause such a scene, then every person would rapidly age right before their death.
Damien's situation was different.
He had just experienced the insurmountable gap between a mortal and someone who had stepped into the realm of godhood.
The gap between 3rd and 4th class was big, sure, but it was nothing in the face of this gap. At the end of the day, both 3rd and 4th class existences existed within the realm of mortals. Even with the Universe Baptism, this fact didn't change.
This was why, as long as he could use external help, Damien still had the potential to kill entry-level 4th class existences.