So this idea is based on some horror tropes.

It's a Post Apocalypse. Most of Humanity is dead, it's been years since most of Humanity died from The Reign of Terror, when the Devil's Son eradicated rival governments and basically took over. Players would be horror trope protagonists.

You can be:
A witch
A demon/human hybrid
A vampire
A werewolf
A ghost
A mad scientist
A necromancer
A ghoul
Maybe something else?

It's up to you if you're good or evil. There are some survivors left, and it's up the players if Humanity survives and restarts civilization or is eradicated entirely.