Secret (2000)

Original title: 비밀

Ji Eun finds out her sister Hee Jung is the daughter of a famous fashion designer and takes over her place as a real daughter. Ji Eun loses her sense of morality as gets into deeper sin out of jealousy toward Hee Jung who also steals both Jun Ho and Young Min's heart. The fashion designer doesn't have the luxury of enjoying the love of her real daughter, Hee Jung when she dies of leukemia. Ji Eun at last realizes unconditional love of this fashion designer and Hee Jung's forgiveness toward her.