I don't get it, why is Makiyo being forced to marry by a royal/noble when she's a commoner? That's what's been bothering me since the start.
eh, the Duke's house took her in, fed her and basically cared for her for a while. He could have said that he adopted her so she's part of the Duke's house, and then by "marrying" (selling) her to the most prospective suitor, he will get power and money. Tbh had the prince and other powerful male figures not been interested in her I doubt he would have kept her for so long. She's basically a merchandise to the Duke.
Also please remember that this was supposed to be an otome game, commoners marrying nobles are common there.