Manga by author Shippo Tanuki - Status ongoing

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...

"Die Instead of Her!'these were the words declared to her by her own father. Cheryl, the count's daughter who had been oppressed by her family, became the sacrifice. By royal decree, her adorable younger sister was arranged to marry the cruel frontier duke. However, Cheryl was ordered to take her sister's place and marry him, only to be killed by monsters on the way to keep the plan hidden! I believed that if I worked hard, I'd be loved someday.' While despairing, Cheryl resolved to accept her fate. But in the forest, she is saved by a red-haired young manher soon-to-be husband, the ruthless frontier duke!? A thrilling Cinderella story of a hated noblewoman's dramatic turnaround begins!"