Keisuke Tanaka, a young man who inherited his deceased grandfather's house, one day discovers the entrance to a 'Dungeon' in a closet in his grandfather's room.

Armed with the EX Skills bestowed upon the very first discoverer of a 'Dungeon,' Keisuke sets out to conquer it.

As 'Dungeons' subsequently appeared across the globe, bringing with them countless boons, the world established the 'Dungeon Seeker's Association.' 'Dungeon Seekers' began to venture into the 'Dungeons,' some for the good of the world, others driven by their own desires.