SNOWBALL EARTH

Tetsuo is a quiet middle schooler whose entire childhood was the giant robot named Yukio that lived with him: built, befriended, and eventually deployed as Earth's last serviceable mecha against the galactic monsters who showed up in the sky a decade ago. After the final battle that put the monsters down, Tetsuo wakes up on the surface to find the planet's geography rewritten into ice. Snow has buried the continents, his promise to Yukio has not been kept, and Tetsuo is the only person currently registered as having survived the war. The series is the search, the cold, and the friend he is supposed to meet again.