BoF II: Black Wing Curse
So according to the legend, a child with black wings born into the royal family would bring a curse upon "the land."
This is where I may have gone too deep in thought:
A young Nina is exiled for her safety, making Mina the heiress to the throne. When Nina returns to the Windia, Mina witnesses the mistreatment of her sister. After Daisy's kidnapping, Nina and the party return to obtain the Mark of the Wing, and learn that the king is gravely ill. It is during this time that Mina learns about Nina's troubled past. At night, Mina steals the Mark and turns herself into the great bird in place of her sister, despite Nina's pleas to not do so.
Mina, the current heiress to the throne, sacrifices her life to turn into the great bird, and with the hyped fear of the curse, the current Windians wouldn't accept Nina has the next heiress. There's no heiress to the throne, and the king is too ill to have another child.
Following these premises, has the curse been fulfilled?