Ja Myung Go

Legend has it that more than 2000 years ago, the Kingdom of Nangnang possessed a mystical Ja Myung Drum (Ja Myung Go) which will sound by itself when enemies invade. In reality, Ja Myung Go does not represent the drum but instead, is embodied by the King's daughter, Princess Ja Myung. Princess Ja Myung and Princess Nak-Rang are born on the same day and time to the same father but different mothers. (mydramalist.com)