Akumyoutakai Ryoushu ni Totsugu Koto ni Narimashita ga Mainichi Shiawase desu

Diana is the daughter of a baron. Her parents have doted on her half-sister so much, that she has grown to be extremely selfish, even stealing away Diana's fiancé! After being made a laughing stock of high society, Diana is forced to marry the brutal and ruthless Margrave Wolfgang. However, the man isn't quite what rumors make him out to be. This is the Cinderella tale of a girl surrounded by sorrow finally finding happiness! (Source: Square Enix)