"Is it my fault you're all in this mess?" yes, yes it is. you started this whole shit in the tunnels to get more coins, you gave the other dude the idea of charging coins for food and even the 100 coins survival fee was the result of your actions! I mean if you're gonna have others die so you'll progress faster, that's fine. but at least have the balls to admit it!
the whole "mild-mannered salary man" instantly turned into "calculative sociopath" is pretty ridicules! there should have been some kind of progression towards that, but nope, he just turned with a flip of a switch at the train! at least the story is interesting!