Ugayafukiaezu no Mikoto "Unfinished Cormorant-Feather Thatching" 鵜葺草葺不合命, commonly shortened to Ugayafukiaezu, is a Japanese (kami) [spirits, not deities], and in Japanese mythology, he is the father of Japan's first emperor, Emperor Jimmu.
Nomenclature and story
In the Kojiki his name appears as Seaside Brave Lad of Unfinished Cormorant-Feather Thatching (天津日高日子波限 建鵜草葦不合命 ama tsu hikohiko nagisa take u ga ya fuki aezu no mikoto?) and in the Nihon Shoki the same name appears with a different spelling.
Ugayafukiaezu was a child of Hoori "Flickering Flame" (the son of Ninigi-no-Mikoto "Ripening Rice-Ears Lad", who was sent by Amaterasu to rule the Earth), and of Toyotama-hime or "Lady Bountiful Soul", a daughter of Ocean Majesty (now identified as the dragon king, Ryūjin).
Although Lady Bountiful Soul became pregnant at Ocean Majesty's undersea palace of Ryūgū-jō, she opted not to bear the child in the ocean and decided to head to shore.
On the shore, the parents attempted to build a house in which she could give birth, and attempted to construct the roof with feathers of the cormorant instead of saw grass. However, while they were finishing the roof, she went into labor.
And so just as she was about to give birth, she spoke to her husband, saying:
"When their time draws near, people of other lands all give birth in the form of their homeland. So I will now give birth in my original form. Please, I beg you, do not look at me!"
Now, thinking these words strange, he sneaked up and peered in at her just as she was about to give birth.
She had become an enormous sea beast many arm spans in length that was twisting and slithering around on its stomach.
In shock and fright at the sight of her, he immediately fled far away.
In shame, the Lady Bountiful Soul fled, leaving behind her newborn, whom she called "Unfinished Cormorant-Feather Thatching" because of her birthing hut.
Later, when Ugayafukiaezu reached adulthood, he married his aunt, Tamayori-hime "Lady Summoned Soul", and they had four children: Itsuse "Hallowed Harvest", Inahi "Rice Spirit", Mikenu "Master Mighty Offerings" and the future Emperor Jinmu, who had several names: Master Plentiful Mighty Offerings, Young Master Mighty Offerings and Boulder Hamlet Lad of Sacred Yamato.
Mikenu traveled to Tokoyo, the "Everworld", and Inahi went into the ocean to be with his mother. The eldest and youngest set forth to rule the land and while they did so together for a time, after Itsuse died, their youngest became the first ruler of earth.