This kind of plot twist feels like something straight out of a gothic novel or a historical drama—maybe something like 'Wuthering Heights' but with even messier family dynamics. I’ve come across similar tropes in old literature, where marriages were often arranged to keep wealth or titles within the family. If the original fiancé couldn’t fulfill the marriage (due to death, scandal, or some other twist), a sibling might be pushed into the role to honor the original agreement. It’s brutal, but back then, personal feelings rarely mattered compared to alliances or inheritance.
In modern storytelling, this scenario could be used to explore power imbalances or societal pressures. Maybe the sister’s fiancé had debts or secrets, and the family saw marrying you off as a way to 'fix' things. Or perhaps it’s a revenge plot—someone pulling strings behind the scenes. Either way, it’s the kind of messy, emotionally charged situation that makes for great drama, though I’d hate to live through it myself.