In the year 2025, huge beasts from beyond the galaxy attacked Earth. In the war that followed, humanity fought back with a giant robot named Yukio, piloted by Tetsuo Yabusame, As the massive alien swarm closed in on humanity's homeworld, Tetsuo and the Earth Defense Force deployed for the final battle with the invading horde. They lost…

Yukio was destroyed in battle and Tetsuo survived in an escape pod. After eight years in cold sleep, the escape pod finally lands back on Earth. But when Tetsuo emerges he finds a world in ruins, entirely frozen beneath a blanket of ice and snow—snowball Earth! What happened to humanity, how did the planet freeze over, and will Tetsuo be able to keep his last promise to Yukio?