A dungeon appeared on the earth that day summary:
One day, a huge dungeon appeared all over the world. Amekawa Firefly, a withdrawal high school student living in Hokkaido, is trapped in a dungeon that appears near her house. Fireflies who managed to return to the ground saw the appearance of a monster that sneaks around the world! Firefly adventure begins to meet the evacuated family. The popular low fantasy from “Become a Novelist” has begun!