Goblin Slayer Side Story II: Dai Katana, Vol. 6 (manga) — Kumo Kagyu

In the abyssal slumber of death, the past flicks by like the lights of a magic lantern… Down, down in the depths of the Dungeon of the Dead, in the innermost of the third floor, six heroes meet their match against frightful masked men. A sharp steel blade passes through a swordsman's throat, and memories of his master through his dying mind…Is this the end of our heroes' mission to defeat the Dungeon once and for all?!