A low-ranked adventurer vs. beautiful A-ranked adventurers!

The A-ranked adventuring party, Deep Emerald, is made up of women who are both strong and beautiful. Galen, a low-ranked adventurer called "demonically foolish" because of his complete lack of magic, begins working for Deep Emerald as an advance guard and gofer in order to pay back his late friend's debts. However, his friend's death as well as the large amount of debt beyond his means were all part of a plot. Galen learns the truth, is abandoned in a dungeon, and almost loses his life by falling into the deepest part of it. However, on the verge of death, he unexpectedly gains power from the master of the monsters and becomes the Dungeon Master...