Underdark: Prisoner Monster Girl Isekai

Synopsis

A young archaeologist, during an expedition, accidentally falls through an ancient portal into a completely alien and dangerous underground world. Without weapons, without friends, and with no idea how to get back home, he finds himself in a brutal reality where humans are a rare and valuable commodity. Now he must survive in a dark fantasy world filled with demons, ancient magic, and creatures that look at him with hungry interest. Gradually, the protagonist begins to realize that there may be no way back… and that this world is slowly but surely changing him.