Ninigi had two sons, the elder Hoderi and the younger Hoori. The elder was Umisachi, Luck of the Sea, who fished the ocean; the younger was Yamasachi, Luck of the Mountains, who hunted in the hills.
One day Yamasachi asked his brother three times, "Let's trade our tools and try," and at last borrowed his fishhook and went to sea. He caught not a single fish, and lost the hook in the sea besides. His brother said, "Luck of the mountains comes with one's own tools, luck of the sea with one's own tools," and demanded the hook back. Yamasachi broke his own sword and made five hundred fishhooks, then a thousand more, and offered them, but his brother insisted, "I'll take nothing but my own hook."
As Yamasachi wept on the shore, Shiotsuchi, the old god of the tides, appeared. He wove a small boat of bamboo with no gaps and put Yamasachi in it. "Ride the current and you will come to a palace roofed like fish scales. That is the palace of Watatsumi, the god of the sea. Climb the katsura tree beside the spring by the gate and wait there."
Yamasachi did as he was told. A maid of Toyotama-hime, the sea god's daughter, came to draw water and was startled to see a beautiful figure reflected in the spring. Toyotama-hime fell in love with Yamasachi the moment she saw him, and the sea god too was delighted, saying, "This is a child of the heavenly gods," and gave him his daughter in marriage. Yamasachi spent three years in the palace under the sea.
Then he remembered the lost fishhook and sighed deeply. The sea god gathered all the fish, great and small, and asked them. They said, "Lately the sea bream has been complaining that something is stuck in its throat and it cannot eat." They searched the bream's throat, and there was the fishhook.
When the sea god gave back the hook, he told Yamasachi to hand it over behind his back, chanting, "This hook is a hook of gloom, a hook of fret, a hook of want, a hook of folly." He also gave him the tide-flowing jewel and the tide-ebbing jewel: "If your brother attacks you, drown him with the flowing jewel; if he begs forgiveness, save him with the ebbing jewel." Yamasachi rode home to land on the back of a wani one fathom long and did as he had been taught. His brother grew poor and came to attack him, but was overwhelmed by the tide and surrendered, and swore to serve from then on as his younger brother's guard.
Aoshima in Miyazaki City is said to be where Yamasachi came ashore on his return from the sea god's palace, and at its center stands Aoshima Shrine, dedicated to Yamasachi and Toyotama-hime. The rippled rock shelves around it, called the Devil's Washboard, make a fitting scene for this tale of the palace under the sea.