"Omae ga Kawari ni Shine" to Iwareta Watashi. Imouto no Migawari ni Reikoku na Henkyouhaku no Moto e Totsugi, Shiawase wo Te ni Ireru

Both my parents had only loved my sister and I had no place at home. I lived my life believing that as long as I worked hard, I would someday be loved. One day, my sister received a royal order to marry a frontier count who was rumored to be ruthless. My father, who loved my sister, said to me, "You will marry into the frontier count's territory instead. But on the way, the carriage will be attacked by demons—you will die." As planned, I was attacked by monsters, but the one who rescued me was the ruthless Count of the Frontier, a beautiful man with bright red hair and sharp golden eyes...