Ryuu stows away on a space vessel, only to be found by the crew when it's far to late to return to Earth. So they stick him in a spare sleep capsule instead. Things take a turn for the unexpected, however, when Ryuu wakes up to find himself the sole survivor of the expedition, the spaceship having crash landed on a grossly mutated and wholly unfamiliar Earth.

Joining forces with fellow survivors from a different crash, Ryuu and his comrades fight to survive on this new and deadly Earth as they search for any humans that might have made it through the mysterious apocalypse.