Randomly remembered a manga I'd come across quite awhile ago that I never bothered too look into outside of reading like half of a chapter, and have since had no luck while searching for it with a friend. From what I remember of the manga it's a slice of life/romance type, and it's essentially about some type of caveman/neanderthal girl in modern Japan, being the love interest of the short mc who can't express himself well to her. I remember there being another girl who actually had some form of sense and talked to mc about interacting with said cavewoman girl, but really nothing else. Sorry if it's vague, but I literally came across some middle or near end part of the series and had no other context to go off.

Also, as of so far from searching, my friend and I can say it's not Neolith Girl or Nadenade Shikoshiko. I've also got a post up on r/manga just trying to cover as much ground as possible, so off chance you see that it's the same guy. Thanks ahead of time, apologies it's such a nightmare.