
If were talking about level, a duke's daughter and an imperial heir can be friends freely considering that a duke family is just one level lower than the imperial family ┑( ̄Д  ̄)┍ so I don't fucking get the audacity of his "fiance" to say "learn your place" to mc though I know that she'll not be a hindrance here but being a fiance of someone who'll lead a freaking country should atleast know the basics. Also, not all type of people can be that close to the imperial heir who at his weak state unless they have a great connection or more like a high status.

Luca and Duke are the same person but in different timeline. Luca is the original version of the duke, he is the person that was able to continue growing that is why he is much mature. Mc is also the reason why he is existing since she awaken him. In the case of the current duke that whom we hate. He is the version of the duke at the timeline when his parents' died. Spoilers said that the immature duke was stuck in sth like his past self that is why he's stupid and immature although we see that he seems aware of the happenings but there is something missing with his decision making. Also, the name Luca came from the Duke's grandfather. He just borrowed it. For the daughter, she's not the Duke's daughter but his niece apparently Rebecca is the daughter of the Duke's sister which was raped by a man during a banquet. Atm, the rapist is still unknown....
but I have a feeling that it is among the imperial family and maybe it could be the emperor himself.
The devil is hot! He already got a reason for me to disregard his personality jk.