When Souhei Saino's parents vanish during a mountain expedition, leaving him alone, his dream of exploring the world as an adventurer seems dashed. Yet, undeterred, Saino remains committed to his goal and gives his all in everything he does. One fateful day, returning home from school, he uncovers a shocking transformation in his basement: once a mere storage space, it has morphed into a vast labyrinth teeming with monsters and treasures. This newfound labyrinth offers Saino the chance to live out his adventurer fantasy, albeit with a peculiar requirement to level up by engaging intimately with any woman he chooses. Armed with magical aids, Saino embarks on a quest to conquer the dungeon, willing to exploit his relationships with the girls he fancies along the way.