ダンジョンで戦い続けて２０年の童貞勇者、地上に戻ったら人口激減男女比１：１０００の世界だった

Welcome to a World with a Gender Ratio of 1:1000!

In the year 199X, labyrinths known as “Dungeons” appeared across the world, bringing forth countless monsters from within. Inside these dungeons, modern weapons ceased to function. The world’s military forces were on the losing side.

In time of peril, Sirius, a self-proclaimed great sage from another world, emerged to save the world from the brink of destruction. Thanks to the divine blessings of a temple he had established, people awakened to magic and skills, which were only usable within dungeons. Those who wielded these powers became known as “Explorers.”

In 2005, through the final operation, an Explorer party succeeded in defeating the Demon King, saving humanity from its crisis. However, one hero remained deep within the dungeon. Yet, the dungeons still persisted across the world.

In 2025, a beginner Explorer by the name Haruka Shimomura found herself in a life-or-death situation during her livestream. She was about to be killed by a high-level monster that should not have existed in the lower floors of the dungeon.. At that moment, the one who saved her was a boy who bore the same name as the legendary hero who had participated in defeating the Demon King’s twenty years ago. He was also the boy who had failed to return 20 years ago.