In 2039, a mysterious structure "sky orbit" appeared in low-Earth orbit. After the sky rails shattered, "grey fire meteors" began to rain down around the world, and dungeon gates contaminated by rules were constantly generated in the city. Humans can obtain "seals", "relics" and "fire" in the dungeon, but those who fail will have the rules rewritten and become alienated bodies. The Kyushu Federation maintains the boundaries of civilization with nine core fire cities. All survivors understand one fact:
It is not humans exploring the dungeons, but the dungeons selecting new worlds.
