Do you want to go outside of the outside?

In the year 2024, the world has collapsed. Grotesque monsters lurk amongst the ruins of Japan, while remaining people scrape together what they can to survive. Kiruko, an odd-job girl in Nakano, accepts a mysterious woman's dying wish to take a boy named Maru to a place called Heaven. Maru is convinced that there will be a boy there who looks exactly like him.