Snowball Earth, Vol. 2 (manga)

Upon his return to Earth, Tetsuo finds the planet frozen over. Much to his surprise and horror, he discovers that the alien kaiju have made it to Earth too. But after meeting a hardy band of human survivors, Tetsuo learns that Yukio has survived as well, his consciousness downloaded into the escape pod—which also happens to be a battle robot! Now headed for the survivors’ stronghold, Tetsuo is determined to make new friends. But the people Tetsuo has found are not the only ones left, and a mysterious humanoid kaiju also lurks among the ruins.