On the way home from a school trip, an unexplained earthquake traps Teru Aoki's express train in a collapsed tunnel. The only other survivors of the catastrophe are his classmates, Ako Seto and Nobuo Takahashi. After the claustrophobic Nobus goes mad Teru and Ako grope their way through to the surface But what awaits them on the outside is a desolate landscape of utter ruin. What could have caused such destruction? A natural disaster? A nuclear catastrophe? A time slip? With mixed emotions of hope and despair, the two head for Tokyo, encountering chaos and anarchy, including a crazed deserter of the Forces, Nimura and a mysterious force called "Dragonhead."