Princess Sapphire is a girl raised as a Prince. Through the mischief of an angel, the princess is born with both a girl’s and a boy’s heart. Since there is no boy successor in her kingdom, Sapphire is raised as a boy, but evil ministers try to reveal her secret. Unable to put up with the kind of vicious conduct prevailing in the kingdom, Sapphire disguises herself as « Princess Knight » and wields her sword of justice.