Into the Deepest, Most Unknowable Dungeon manga volume 11 features story and art by Kakeru.

Jean and the girls stumble upon the waterlogged remains of an ancient underground civilization…and encounter the many-headed hydra! But these are no mere beasts—more heads means more brains, and soon it is siege tactics and war between humans and cunning, nigh unkillable, monsters! No magic! No cheats! Get balls deep in this isekai adventure, where intelligence and instinct collide!