The Fallen Guardian. An archangel, overpowered by Hell.

Guardian of Gehenna

This guy is a really sad final boss

from what you've told me he sure sounds like it

Yes

Imagine having to fight for the thing you were meant to destroy

As rot degrades your body

And your body acts on itself due to the rot, but being unable to do anything at all, just witnessing everything

unpleasant

He can also feel all the pain

uncomfortable