ある日、巨大なダンジョンが世界中に出現した――。北海道に住む引きこもり高校生の雨川蛍は、家の近くに出現したダンジョンに閉じ込められてしまう。何とか地上に戻った蛍が見たのは、世界を跋扈するモンスターの姿! 避難した家族に会うために、蛍の冒険が始まる。「小説家になろう」発の大人気ローファンタジー、開幕! 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!