How to make a story have a lonely, dark, depressing atmosphere to it?

I'm starting a new manga (Graphic Novel) and I need to make the story have a lonely, depressing feel to it. The basic plot of the story is there is a bomb that wipes out most of the human race, and the main character and a couple of other characters are trying to survive, in the end, the main character will eat a couple of the other characters, and some will go insane, and commit suicide. Help!

Answer: 
It was a dark and stormy night...