The Tale of the Sea Prince and the Mountain Prince (Umisachi-Yamasachi)

After Ninigi's descent and marriage to Konohanasakuya-hime, she bore three sons in the fire-trial of her innocence. The eldest was Hoderi, called Umisachihiko (Sea-Luck Prince), who made his living by fishing; the youngest was Hoori, called Yamasachihiko (Mountain-Luck Prince), who hunted in the mountains.

One day, the brothers agreed to exchange their tools and try each other's trade. Hoori took Hoderi's cherished fishhook to the sea, but despite his efforts, he caught nothing and lost the precious hook in the waves. When he returned empty-handed, Hoderi was furious and refused to accept any substitute—even five hundred newly forged hooks. He demanded the original back.

Despairing, Hoori sat weeping on the seashore when the wise deity Shihotsuchi appeared and set him on a path to the palace of the sea god Watatsumi. Placed in a small woven boat, Hoori descended through the waters to a magnificent undersea palace draped in coral and gems. There he sat by a well beneath a cassia tree, and when the sea princess Toyotamahime's attendant came to draw water, she noticed the handsome stranger. Toyotamahime herself came to see him, and the two fell in love.

Watatsumi received Hoori warmly. For three years, the young prince lived in luxury in the undersea palace with his bride. Eventually, remembering his original purpose, he asked the sea god for help finding the lost fishhook. Watatsumi summoned all the fish of the sea, and the hook was found lodged in the throat of the sea bream (tai). The sea god gave Hoori the hook along with two magical jewels—the Tide-Raising Jewel (Shihomitsutama) and the Tide-Ebbing Jewel (Shihofurutama)—and instructed him in their use.

Returning to the surface world, Hoori confronted his brother. Following the sea god's instructions, he returned the fishhook with a curse upon it. When Hoderi tried to fish, his catch only diminished. When he tried to farm, his fields dried up. Desperate, Hoderi attacked his brother, but Hoori raised the sea with the Tide-Raising Jewel, nearly drowning him. When Hoderi begged for mercy, Hoori lowered the waters with the Tide-Ebbing Jewel. Utterly defeated, Hoderi pledged to serve his younger brother forever as his guard.

Toyotamahime came ashore to give birth, building a parturition hut thatched with cormorant feathers. She warned Hoori not to watch the delivery. But driven by curiosity, he peered inside and saw that she had transformed into a great wani (sea creature)—her true form, revealed in the vulnerability of childbirth. Ashamed and heartbroken that her secret was exposed, Toyotamahime returned to the sea, sealing the path between land and water. But she could not abandon her child, and sent her sister Tamayorihime to raise him.

The child, named Ugayafukiaezu ('the one born before the cormorant-feather roof was finished'), would grow up to marry Tamayorihime herself, and their fourth son would become Emperor Jimmu—the founder of the imperial dynasty.