Backstabbed in a Backwater Dungeon: Volume 3 (Light Novel) oleh Meikyou Shisui

Fresh from getting revenge on the elf who put an arrow in him on that fateful day, Light learns that another of his betrayers, the dark elf Sionne, is in grave danger. While conducting experiments on Gifted humans in her underground lab, she accidentally summoned a soul-eating dragon that has transformed her lab into a vast dungeon. Light now has no choice but to rescue her if he wants to get even with his old foe. So, in his guise as leader of the Black Fools, Light teams up with a party of dark elves led by Yude, a high-ranked adventurer who’s taking point on a quest to wipe this new dungeon off the map. But there’s more to Yude than meets the eye, and Light soon finds out that this potentially world-destroying dungeon isn’t the only threat he’s up against. Can Light navigate the liminal space between the worlds of the living and the dead to get revenge on Sionne before she dies some other way?