(Havent thought of one :( sorry)

The story of a man named Arstum, born and raised in the subway tunnels of a city not even he knows. A vast plague of toxic gasses and vile beasts upon the city makes it near impossible to travel to the overworld. A term now used to describe the emptiness that is now the destroyed city... And the home to the most ravenous creatures ever to roam the earths land, and those are just the small ones.