Ryuu no Michile Voyage de Ryu, The Road of Ryuu, The Way of Ryu

Ryu 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 Ryu 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, Ryu and his comrades fight to survive on this new and deadly Earth as they search for any humans that might've made it through the mysterious apocalypse.