Kowareta Sekai no Mukougawa

Fuu is a lonely girl from the lowest stratum of life. Her only friends are Asa, a little bird, and an old radio she found in the corner of a junk shop. Then there is Kazakura, a hungry girl who goes at her own pace. From the moment they first meet, she calls Fuu "big brother" and follows her around with a cheerful smile. The place where they meet is the only remaining human country in the world. In the middle of an endless desert ruled by deformed monsters, human beings must live for the king, the messenger of God, taking pleasure in daily hardships. But the world they know is all a big lie. With a lot of wisdom and a handful of courage. Now, the "world's heaviest escape drama" begins. (Source: Kadokawa, translated)