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, a boy barely old enough to go to school. Ten years later, the massive alien swarm closed in on humanity's homeworld and 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, and Tetsuo awakens, determined to fulfill his promise to his comrade in arms that he would live his life to the fullest and make many friends. But what he finds instead is a world in ruins, entirely frozen beneath a blanket of ice and snow, it's a snowball Earth! What happened to humanity, how did the Earth freeze over, and will Tetsuo be able to keep his last promise to Yukio?