Betrothed to My Sister's Ex (Indonesian Dubbing Project)

The Shaderan family has fallen on hard times, and the avaricious and callous baron and baroness will stop at nothing to regain status. They favor their beautiful daughter Anastasia, hoping to marry her into wealth, while they treat the second daughter, Marie, no better than a servant. Years of abuse have convinced Marie that she is truly undeserving of love and attention.

On Marie's birthday—used as a ploy to showcase Anastasia—Marie meets Count Kyros Granado, who is immediately charmed by Marie and her knowledge of his culture. Believing Anastasia to be the one he fell for, Kyros proposes via letter. But Anastasia tragically dies on her way to marry him.

Forced to take Anastasia's place, Marie becomes Kyros' fiancée, just as he originally intended. Although Marie terribly lacks confidence, Kyros gently helps her find her worth, awakening her to her own beauty and the true meaning of being loved.

Synopsis Source from MyAnimeList