Goblin Slayer Side Story II: Dai Katana, Vol. 1 (light novel)

Not so very long ago, the Death began stalking the continent. The King of Time issued a proclamation: “Find the source of this Death and seal it away.” The source: the Dungeon of the Dead. A fortress city that arose at the mouth of the dungeon serves adventurers who seek companions, challenge the dungeon, battle, find loot… and sometimes die.
You are an adventurer who has come to the fortress city in hopes of reaching the dungeon’s lower- most depths-but can you and your party conquer the untold evils that lurk beneath the surface?