OC lore:

Satan (the cat) intentionally has no lighting / shading as he is basically a void that consumes all light that touches him. He likes to pretend to be a cat cos- who wouldn't trust a cat?

The other guy is Marcus, a human incarnation of an angel named Ophaniel who wrongfully became fallen, his human self is- a huge fucking moronic jerk, and its made even worse cos Satan and the dude who made him become fallen, Phanuel, like to show up and offer him "advice" every once in a while

Marcus has no memories of being an angel, as angels who become humans lose it until they die again- since humans' personalities are based a bunch on their childhood and brain chemicals, they can be SUUUPER different personality wise and all from their angel self.

Marcus does not believe anything about being an angel, thinks these two (and possibly even himself) are going nuts, and just wants to be left tf alone, however, they do have SOME influence on him despite this. He likes to trip out and experiment with all sorts of substances, so sometimes he blames those, but other times, he will accept the fact there's a talking cat haunting him but try his best to just ignore it and tell it to fuck off.

Angels who fall have 1 chance to come back to heaven by serving a trial in which they live a pure human life. Satan and Phanuel are both sabotaging this chance- but Satan is the one who convinced him to do this trial almost right away in the first place, as he can see future possibilities (I hate Steven Universe, but it works kinda in the same way it does with Garnet from that show IG?) and he knew that Ophaniel would eventually end up in hell after failing his trial and become- basically a suuuuper strong puppet.

This pic is just Satan bothering Marcus as he casually does throughout his trial.