The Princess/Origin

Origin
Toyotama-hime (meaning "luminous jewel"), also known as Otohime, is a goddess in Japanese mythology. She is the beautiful daughter of Ryujin (meaning "dragon god"), the god of the ocean. She married the hunter Hoori and gave birth to a son. Her grandson is said to be Emperor Jimmu, the first Emperor of Japan. During the time when Otohime was giving birth to her child, she had Hoori swear not to attempt to see her real figure. But he broke his promise and discovered that her true form was a dragon.

Otohime appears in Urashima Taro, one of Japan's best known myths. Urashima Taro was a young fisherman who saved a small turtle from torture at the hands of a gang of children. It turned out that the turtle was Otohime. He was rewarded with a visit to Ryujin's palace under the sea. He spent 3 days at the palace with Otohime (who shapeshifted to human form). When it became time for the fisherman to return home, Otohime gave him a small box. She told him that the box will protect him but that he should never open it. When the fisherman returned to his village he realised that 300 years has passed. His family, friends and everyone he ever knew was gone. Desperate, he opened the box and instantly became an old man.

- It seems that Dragon Princess is not Toyotama-hime, although Toyotama-hime is a dragon princess. Info transfered from Dragon Princess.