Ugayafukiaezu-no-Mikoto (鵜葺草葺不合命?), commonly shortened to Ugayafukiaezu, is a Japanese deity (kami) and in Japanese mythology, he is the father of Japan's (mythical) first emperor, Emperor Jimmu. In Kojiki, his name appears as Amatsuhitaka-hiko'nakisatake-ugayafukiaezu-no-Mikoto (天津日高日子波限 建鵜草葦不合命), and in the Nihonshoki he is called Hiko'nagisatake-ugayafukiaezu-no-Mikoto (彦波瀲武鸕鶿草葺不合尊).
Ugayafukiaezu was a child of Hoori, a son of Ninigi-no-Mikoto, and Toyotama-hime, a daughter of Ryūjin. Though Toyotama-hime became pregnant at Ryūgū, the undersea palace, she opted not to bear the child in the ocean and decided to head to shore. Both Hoori and Toyotama-hime attempted to build a house in which she could give birth, and attempted to construct the roof with feathers of cormorant instead of saw grass. However, while they were finishing the roof, she went into labor. So the child was named Ugayafukiaezu (lit. the roofing cormorant alternative to saw grass was not in time).
While in labor, Toyotama-hime said to Hoori, "people in other countries change back to their original form when delivering a child. Because I think I too am changing back to my original form, do not look in the house no matter what, while I am delivering the child". However, Hoori looked in the house and saw Toyotama-hime in her original form of a shark, and he fled. Feeling shamed, she returned to the sea, leaving her newborn child behind and sending her younger sister Tamayori-hime to raise the child in her place. Another take on the legend states that feeling completely humiliated, she rushed back to the sea, dropping the child on the shore; the cries of the newborn infant reached Tamayori-hime's ears and she opted to raise the child instead.
Later, when Ugayafukiaezu reached adulthood, he married Tamayori-hime, and they had four children: Itsuse-no-Mikoto, Inahi-no-Mikoto, Mikenu-no-Mikoto, and Kan'yamato Iwarebiko. Mikenu traveled to Tokoyo (lit. "the normal world", though some texts hint that it is the afterworld), and Inahi went to the ocean to be with his mother. Kan'yamato Iwarebiko, their youngest child, would later become Emperor Jimmu.