>>280178150
I prefer the teacher (the black haired butt one). I don't know much about the LN. It seems to be on hiatus. I hope it is a harem ending. The wiki mentoned the teacher (black haired one) as being a member of the harem but only as love interest while the others are mentioned as his girlfriend.
https://the-hidden-dungeon-only-i-can-enter.fandom.com/wiki/Noir%27s_Harem
Rit is also very hot with her boobs and blonde hair but I prefer Ruti in that anime.