Ribbon no Kishi

Prince Sapphire is a girl, which is a major secret in the realm of Silverland. Sapphire unintentionally inherited the blue heart of a boy and the pink heart of a girl when she was born. Sapphire lives a double life, pretending to be a boy because women are not permitted to hold the monarchy, in order to preserve the nation from the evil Duke Duralumin, who is the heir to the throne. Sapphire's boy heart is being sought for by Tink, a young angel, but Sapphire won't let go of it. Sapphire finds herself in an even worse situation due to the conflict between her two identities when she falls in love with Prince Franz Charming from the neighboring kingdom as the Duke plots to steal the throne. Sapphire and Tink are now off on fascinating adventures, but they must face many foes in order to maintain the monarchy at all costs.