I don't see what's that confusing in the first place.
She was chosen as a pretend fiance, he wasn't looking for a lover in the first place. Every action of the characters is pretty obvious(1. he gives her a task to kind of tease her, he says it himself 2. he is impressed with her dedication and skills, which is why she gains his trust (her personality is also one of the reasons) 3.the fl is kinda nosy and she takes everything seriously........)
Also when it comes to his red eyes, they're still just hinting that duke isn't an ordinary person(in the last ch16 was a pretty obvious hint that the duke is of different race or mixed). They're not gonna tell you straight out why are his eyes red lol
This are all very common tropes.
I don't want to drown you with info, but maybe you should reread the story on your own, now since it's still only 16 chapters
For me me the evolution of the plot doesn't make sense. As I said it's my opinion...you are yours too and I respect it
I completely agree that the plot is lacking. However, I would like to say that I am confident the ML's red eyes will be explained later. There are already several hints that the Duke is not human, considering this world also contains various supernatural and fantastical species.
What with that story? She was chosen to play the fiancee role without any feelings involved...but now she is involved in politics, the Ml isn't enough cold or respect is own beliefs...red eyes were brushed over without a bit of explanation and he has a hearing non human...wtf author are you mocking us?