i really doubt that the sibling is the fl because like for starters the main character seems to be scared of her? based off of the nightmare at least. he didn't seem to think that the nightmare was that farfetched and the story is that hes running away from marrying her. if she ended up being the fl that would make his journey pretty much worthless because no matter what happens or who he saves his end goal was for his sister and family to give up on marrying him to his sister. so yeah
i really doubt that the sibling is the fl because like for starters the main character seems to be scared of her? based off of the nightmare at least. he didn't seem to think that the nightmare was that farfetched and the story is that hes running away from marrying her. if she ended up being the fl that would make his journey pretty much worthless because no matter what happens or who he saves his end goal was for his sister and family to give up on marrying him to his sister. so yeah