Help me fing this old treasure

So a really long time ago I read this manga and can't remember it to well but something I do remember is the monster looking similar to the one in "monster child". The plot of the manga (idk the name of ) is kind of like the place where people are sent and they have to try to survive with the monsters in there I think it was like a science experiment. The story really focus on a a dark haired girl with glasses I believe and a man with kinda long dark hair who is really buff and scary looking. If you have any idea of what I might be talking about pls let me know. I don't think it was a popular manga though I could be wrong