Ryusuke Shiomi

Princess Sapphire is a girl raised as a Prince. Through the mischief of an angel, the princess is born with both a girl's body and boy's mind. 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.

5000 years ago, the Triton Family was living peacefully in Atlantis until the Poseidon Family destroyed them all. Triton, of the Triton Family line, embarks on an adventurous life in the sea fighting the Poseidon Family.