Tales of the Tendo Family, Volume 1 (Tales of the Tendo Family #1-4)

Masato, a son of the Tendo family, is meant to marry Hojo Ran, the daughter of a baron. There's just one problem: she's a fake. The real Ran has fled after hearing that few make it out of the Tendo family alive. In her place is a young woman who says she will die if it means saving someone else's life.