During the Age of the Gods, the daughter of the Japanese sea King Ryujin, Toyotama, lived with her father in the underwater palace of Ryugu-jo. One day, the dragon goddess met a young hunter named Hoori who had come to the bottom of the ocean looking for a missing fishing hook that belonged to his brother. The two fell in love and were married.
After a few years of living together in the palace, Hoori began to long for a life above the sea. He convinced Toyotama to come with him and, pregnant with his child, she agreed. They set up camp inside a cave along the shore and soon after Toyotama went into labour.
Not wanting her husband to see her transform into her alternative form, Toyotama begged him to wait outside. Curiosity got the better of him, though, and he peered in to find a giant black dragon holding a baby. Ashamed, Toyotama fled back to the sea, leaving her breasts behind to feed the newborn child.