Shy Tetsuo Yabusame and his only companion, the giant robot Yukio, fought as humanity's saviors against monsters invading from outer space, until Yukio was destroyed in the final battle and Tetsuo survived in an escape pod. After years in cold sleep, the pod finally lands back on Earth, and Tetsuo steps out into a world in ruins, frozen entirely beneath ice and snow. With no idea what happened to humanity or how the planet froze over, he sets out across Snowball Earth still holding on to his last promise to Yukio: that he would make a friend.