The Shell.

In a dystopian future, the world is suffering from overpopulation. A group of radicals calling themselves the "Enthusiasts" are trying to prove the Myth to the world. The Myth is the world they are living in is inside of a shell, and there is a bigger and unknown world outside of it. Will, a depressed and cynical assassin, is determined to kill the leader of the Enthusiasts. But when he fails to kill a young Enthusiast, he begins to question whether or not the Myth may actually be true.