Goblin Slayer Side Story II: Dai Katana, Vol. 1 (manga): The Singing Death — Kumo Kagyu

The impregnable Dungeon of the Dead lies in the farthest north, spewing the Death from its gaping maw, a plague of devastation and undeath that has spread throughout the Four-Cornered World. Nothing but certain doom has awaited those who descend to its deepest level in hopes of finding the source of this pestilence -- at least, not until that challenge is met by a certain party of adventurers, six men and women who would one day be called heroes...With this volume, the ashen tale of the legends of Goblin Slayer's world begins!