The one mystery I'm most curious about are the girls who don't get rings after he has sex with them.
Like what makes them different in comparison to the other girls. I'm also curious about where the girls come from. Since there aren't any men, and the main heroine said they come from the castle, I'm thinking that maybe some of the girls are born biologically while some are cultivated in vats. Maybe the girls who are born biologically don't get rings and the ones cultivated in vats do.
The weird time-traveling stuff is also getting to me. Why does Youta travel only when he dies? Why could nobody else see the bear that killed him and why was that bear able to physically interact with him.
I hope this isn't like Brynhildr of the Darkness where MOST of the mysteries are answered in the last 5 chapters.