Is It Wrong to Try to Pick Up Girls in a Dungeon?, Vol. 10 (light novel) — Fujino Omori

After encountering intelligent monsters in the Dungeon, Bell and Weine share a tearful goodbye as Hestia Familia return to the surface short one member. But not long after their parting, the Guild confirms the existence of armed monsters and immediately calls on Orario's strongest to exterminate this threat. Bell is forced to make some of the hardest decisions of his life when he's the only thing standing between a massacre of monsters and adventurers.