This might fit well in a mob setting. I generally detest mob stories, but it could be two "families" solidifying the end of a generation of fighting and bloodshed with a marriage. The girl is the oldest sibling, and her younger brother is worried that her husband might take his place as head of the family, so she’s worried about him causing said disaster. Then she stops him somehow, or he dies, or falls off a bridge, or becomes a Shinto pacifist vegan, or something, and then the disaster is averted. And then you can put in another twist: the girl he decides to marry instead of the main girl is her cousin, or younger sister. *twist!* Or not. The mob is also good background for future stories, and there’s a lot of material available for building the setting.

But like I said, I hate mob stories. I feel dirty for suggesting this.