Prompt: To create a post-war world where people do not have a stable place to live. The buildings on the ground were destroyed by the shells, and only deserts, seawater, ruins, and burned plants were left on the ground, so people left the ground and turned to live underground, and collectively lived in underground shelters, and began to build cities underground, and the underground world was bright, with buildings, buildings, green spaces, clean water, and so on