First, a Dungeon had appeared at the city of Niarki and a monster rampage had occurred, causing a great deal of panic.

The monster rampage and the Dungeon, named ‘Heinz’s Skeleton Cavern,’ had been dealt with by the A-class adventurer party, the Five-colored Blades. After the Dungeon was explored, it was declared to be a C-class dungeon with thirty floors and that monsters shouldn’t emerge from within as long as the monster population inside was periodically kept in check.

Apparently, there were many Undead, venomous insectoid monsters and poisonous plant-type monsters; most of the floors were caves, swamps or forests.

During the monster rampage, all of the monsters had been more powerful than their Ranks, but the monsters had now returned to normal strength.
But it seemed that when the Blue-flamed Sword Heinz entered the Dungeon, the monsters would flood towards him.

This was a chance for the city of Niarki, especially the Adventurers’ Guild, as only small-to-medium-sized Devil’s Nests and D-class Dungeons had existed nearby until now. The monsters that appeared in the new Dungeon were unique, so the Dungeon wouldn’t be very popular, however.