The Beauty Double / Her Perfect Replacement

Because the female protagonist and her stepsister look similar, she is forced to consummate the marriage with the military governor on behalf of her stepsister who is currently unable to do so. However, it turns out that the seemingly-pitiful protagonist is actually a determined woman with a plan to avenge her mother. She wants to take this chance as a "sleeping tool" to become the real wife of the governor, win the governor over, and take away everything from her stepmother and stepsister! Amid the thorny circumstances, she fights with her decisiveness and intelligence, and develops a pure romance with the governor. Ultimately, she gets her revenge and turns the table magnificently.