He Begged, She Walked.

The daughter of a gang boss saves a rival gang leader and assigns him to be her bodyguard; however, through a twist of fate, he mistakenly believes it was her stepsister who saved him and falls in love with the stepsister instead. Heartbroken, the female lead leaves and takes her stepsister's place in a marriage to the president's son—who has gone blind and lost his political prospects—while the stepsister marries the gang leader.