There are several of these stories in existence, and nearly all of the islands have some minor detail different here or there. However this is the origin story that I put together based on the Chuzan Seikan (中山世鑑) from 1650, Kyuyo Gaikan Irosetsuden from 1745, and the Ryukyu Shintoki from 1608. The Chuzan Seikan is the Ryukyu Royal court document, and there was a lot of outside influence in it, so that is why I used the other two documents to supplement the story to try to bring it back to the original Okinawan folklore vice a court approved version that added in Japanese, Chinese, and Korean elements.
Enjoy - Gambatte Kudasai!!!
In the beginning the world was void. The giant named Amanchu rose from the depths of the void and divided Heaven and Earth. As aeons passed the world caught the attention of the Sun God who lived in obotsu kagura (the other realm). The Sun God and Heavenly Emperor Tedako Onushi saw Earth and thought it would have potential. So he sent his heavenly daughter, Amamikyo (アマミキヨ), to earth. Amamikyo took no time to pull islands out from the abyss, and came from heaven and then stood on earth at the Sefa utaki (斎場御嶽). She covered the islands with rocks, soil, plants, flowers, and trees. Satisfied with the results Amamikyo went back to the heavenly palace and begged her father for hitodane. He granted her wish and the hitodane was placed on Hama Higa island, and Amamikyo and her husband (or brother) Shinerikyo (シネリキヨ) went to earth and their spirits filled the hitodane, and they became human.
The Sun Goddess Amaterasu stayed in the heavenly palace so she could watch after her children, as Tadako Onushi would travel back to obotsu kagura. She would cross the sky each day and settle into a great cave called kumayaa in the evenings. In the mornings she would come from the water by Iheya-jima and trek across the sky to watch her children grow.
As the children grew into adults food became scarce, so a giant bird brought 5 grains from nirai-kanai (underwater dragon palace, past Kudaka island) and dropped them on Kudaka jima and around Chinen and Tamagusuku. The two divine children then began growing food from the soil in a spot between the Ukinju (受水) and Hainju (走水) springs.
Time passed, and one night when Amamikyo was in her hut, a passing wind impregnated her. She had five children. The first child was a boy, and he became first of the line of kings. The second child was also a boy; he became a great hunter and warrior. The third child was a daughter and she became a high priestess (Noro) and was set to advise her brothers in all matters. The fourth child was a boy, and he took interest in the grains, and became a farmer so he could supply food for his family. The fifth child was a girl, and she became a shaman (Yuta).
According to the Irosetsuden (遺老説伝), the family needed to be able to warm themselves and to cook, so the oldest daughter went to nirai kanai and confronted Ryugu (竜母) the dragon who controls the seas. From Ryugu she brought back the secrets of the sacred fire.
All was right in the world. So the oldest boy, Tentei, declared himself the king of the island, and the Tenson dynasty (天孫王朝, the Heavenly Descent dynasty) began with the grandson of the sun god and lasted for 17,000 years and 25 kings.