Ugayafukiaezu is a deity in Japanese mythology. This deity is referred to as 天津日高日子波限建鵜草葺不合命 (Amatsuhiko hikonagisatake ugayafukiaezu no mikoto) in the Kojiki (The Records of Ancient Matters), and 彦波瀲武草葺不合尊(Hikonagisatake ugayafukiaezu no mikoto) in Nihonshoki (Chronicles of Japan).
He was the son of Hoori (Yamasachihiko), his father, and Toyotamabime, his mother who was the daughter of Watatsumi no kami (the sea god). Three generations of deities, including Ninigi, Hoori, and Ugayafukiaezu, are called Himuka sandai or Hyuga sandai.
Although Toyotamabime, the daughter of the sea god, became pregnant at Ryugu (the palace of the dragon king believed to exist at the bottom of the ocean), she went up on the land as she thought it was inappropriate to give birth to a child of Tenjin (the heavenly god) in the sea. Although she tried to make a shelter on the beach, she went into labor before she could completely thatch the roof with waterfowl feathers which she used instead of the usual grass. Hence the newborn baby was named 'Ugaya fuki aezu,' which literally means being unable to 'finish thatching the roof with waterfowl feathers'. Toyotamabime said to Hoori, her husband, that women from different countries turned into their real selves when giving birth. She told her husband not to look into her maternity room as she wanted to assume her real self to deliver her baby. Despite her plea, Hoori peeked in her room only to see a giant alligator, her true self, crawling around. He ran away. Ashamed of being seen by her husband Toyotamabime went back to the sea, leaving her newborn baby behind. Then, she sent her younger sister, Tamayoribime, in her place. Although Toyotamabime was angry with Hoori for having peeked into her delivery room, she still felt great affection for him. She exchanged poems with him through Tamayoribime.
Ugayafukiaezu, when he grew up, got married to Tamayoribime, his fostering mother, and had four children with her: Itsuse no mikoto, Inahi no mikoto, Mikenu no mikoto, and Wakamikenu no mikoto. Mikenu went over to Tokoyo (lit. "the normal world," though some texts hint that it is the afterworld), while Inahi went to the ocean where his mother resided. His youngest child, Wakamikenu, who later became Kamu yamato ihare biko, was Emperor Jinmu, the first Emperor of Japan.
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One gets married to someone of a different species and is told that a particular action is taboo, but the taboo is broken and the true self of the partner is revealed. The couple are forced to separate. Stories of this type are common all over the world. They are often found in Japanese mythology as well, (as seen in tales of visiting Yomi, a world after death, to give birth to a deity). The Grateful Crane, a folktale, also has a similar plot. Amongst them, the offspring of children who were born from the parents of different species are often described as the earliest ancestors of the imperial family and noble clans.
All the deities that are connected to Emperors, except for the deity Ugayafukiaezu, have names related to the 'rice plant.'
Many scholars hold different theories on the reason for this. Some say that Ugayafukiaezu might have been a deity created at a later time as there have been few descriptions of his deeds and achievements. They consider that Ugayafukiaezu, a deity who combines the power of mountains and the sea, might have served as a symbol of the Emperor who ruled everything, from mountains to the ocean.
Furthermore, according to some ancient historical records and legends, including "Uetsufumi" (Ancient Japanese Literature) and "Takeuchi-monjo" (an ancient text that recorded the lineage of ancient deities and a dynasty preceding Emperor Jinmu), Ugayafukiaezu is depicted as a dynasty (the Ugayafukiaezu dynasty) that lasted tens of generations, not as a deity. Some say that Ugayafukiaezu is the same as Tentsushi, who appeared in a tale of Yashiro-go (Yasugi City, Shimane Prefecture) in Izumo no kuni fudoki (the topography of Izumo Province).
Like other deities connected to emperors, Ugayafukiaezu is worshipped as a deity of agriculture. Because of the tale mentioned earlier, Ugayafukiaezu has also been prayed to as a deity to whom people pray for matrimonial harmony and safe childbirth. Ugayafukiaezu is enshrined in Udo-jingu Shrine (Nichinan City, Miyazaki Prefecture) and Miyazaki-jingu Shrine (Miyazaki City).
According to the Nihonshoki, Ugayafukiaezu was buried in a placed called 'Aira no Yamanoue no Misasagi' (literally, Imperial Tomb at the Top of Mt. Aira). However, there are many places in Southern Kyushu that have been believed to be the burial place of Ugayafukiaezu. In 1874, the Meiji government determined that his tomb is located in Kanoya City Kagoshima Prefecture (formerly Aira-cho, Kimotsuki-gun), based on the opinions of the scholars of the defunct Satsuma Domain.
(The government also identified tombs in Kagoshima Prefecture as those of the other Himuka sandai deities.)
However, as opposition to this decision came from people in Hyuga a survey was conducted by the scholars of ancient Japanese literature and culture and the Imperial Household Agency. In 1896, a decision was finally made on this issue that the top of Mt. Hayahi-no-Mine, which is located behind Udo-jingu Shrine, is the legendary place of 'Aira no Yamanoue no Misasagi,' the tomb of Ugayafukiaezu. There are some scholars who still insist that the tomb is located in 'Aria no Yamane no Misusage' in Takachiho Town, Nishi usuki County, Miyazaki Prefecture.