Every Japanese emperor since the eighth century has been officially descended from a deity who came down a mountain in Kyushu carrying three objects and immediately made a decision that guaranteed his own descendants would die. Ninigi's career is short, and both halves of it are constitutionally significant.
The wrong grandson
He was not the intended candidate. The heavenly kami resolve that the land, once surrendered by Ōkuninushi, should be ruled by Amaterasu's son Ame-no-Oshihomimi. He sets out, looks down, reports that the place is in an uproar, and goes back. By the time the ground has been prepared, he has fathered a son and nominates him instead.
So the descent — tenson kōrin, the descent of the heavenly grandson — is a substitution, and the chronicles say so plainly. His full name is a garland of epithets about abundant rice ears and ripening, which is what nigi is generally taken to signify: he is a harvest.
Amaterasu sends him with an escort of five clan-ancestor deities, including the ritualist Ame-no-Koyane, forebear of the Nakatomi and thus of the Fujiwara who would run the country for centuries. The descent is a founding charter for the whole aristocracy, not just for the throne.
What he carries
She gives him the mirror with an instruction that shapes Japanese religion: to revere it exactly as he would revere her, and to regard it as her own spirit. That is the sanction for Yata-no-Kagami at Ise, and for the mirror in the sanctuary of shrines generally.
With it go the curved jewel and Kusanagi, the sword taken from the serpent's tail. The three together are the sanshu no jingi, the imperial regalia, and their transfer is the moment they become that. No enthronement since has been valid without them.
At the crossroads of heaven the party is blocked by an enormous glowing kami, and Ame-no-Uzume is sent to deal with him; he turns out to be Sarutahiko, waiting to act as guide. Ninigi then pushes through the eightfold clouds and comes down onto a peak called Takachiho in Himuka, in southern Kyushu, and remarks that the place faces the land of Kara and the cape of Kasasa and gets good morning and evening sun.
Two mountains, one name
Where Takachiho is has been argued for centuries and is still argued locally. Two Kyushu sites claim it: Takachiho-no-mine, a volcanic peak in the Kirishima range on the Kagoshima–Miyazaki border, served by Kirishima Jingū; and the Takachiho gorge area in northern Miyazaki, with its own shrine complex and a celebrated nightly kagura. Both have long traditions, both have shrines of real antiquity, and the chronicles do not contain enough geography to settle it.
The wider question of why the descent happens in Kyushu at all, when the state that commissioned the chronicles was centred hundreds of kilometres north-east in Yamato, is more interesting. The narrative then requires the descendants to campaign eastward — Jimmu's expedition — to reach the place they actually ruled from. A myth invented purely to justify Yamato would not have started in Kyushu. Something is being accommodated there, and what it is remains open.
The choice that made people mortal
He asks the mountain deity Ōyamatsumi for his daughter Konohanasakuya-hime, the blossom princess. The father, delighted, sends both daughters — and the elder, Iwanaga-hime, whose name means enduring rock, is so ugly that Ninigi sends her straight back.
Her father's reply is the aetiology. He explains that he offered the two together deliberately: with the rock-daughter, the heavenly grandchild's life would have been as lasting as stone; with the blossom-daughter, it would flourish like flowers. By returning one and keeping the other, Ninigi has chosen brevity. From that day, the Kojiki says, the lives of the sovereigns have been short.
It is a mortality myth of a very specific kind. Humans here do not lose immortality by eating something forbidden or angering a god; they lose it by preferring beauty to durability, and the loss is inherited from an ancestor's aesthetic judgement. Iwanaga-hime is enshrined at Kirishima and elsewhere, and is petitioned, with unmistakable irony, for long life.
The rest is genealogy
His sons include Hoderi and Hoori, whose quarrel over a lost fishhook takes Hoori to the palace of the sea deity and generates the line that continues to Jimmu, conventionally counted the first emperor. Ninigi's own subsequent life is not narrated. He arrives, receives the regalia, marries, fathers the line and stops.
He is enshrined at Kirishima Jingū, at Nitta Shrine in Satsuma, and at Tsukuba and elsewhere, but he has no substantial popular cult. The comparison with Hachiman is instructive: a deity with real doctrinal weight and few worshippers, against one with thin mythology and forty thousand shrines. Structural importance and religious popularity are almost unrelated in this tradition.
The descent, restaged
He is not a common figure in games or anime, which prefer the storm and the fox and the sun. Where the descent does appear, it is usually as an image rather than a plot — a figure coming down through cloud with three objects — and it turns up as such in ceremonial art, on shrine ema, and in the visual language of a great many "chosen heir" openings.
The 2019 enthronement of the present emperor brought the material into live broadcast: the Kenji-tō-Shōkei-no-Gi, in which the sword and the jewel are presented, is the ceremony that Ninigi's inheritance is understood to establish. That the mirror stays at Ise and does not travel is itself a piece of the same mythology.
Why do the regalia include a mirror rather than a crown?
Because what is being transferred is not sovereignty in the European sense but presence. Amaterasu's instruction attaches her spirit to the mirror, which makes the object a proxy for the deity rather than an ornament of office, and the same logic operates in every shrine sanctuary in Japan, where a mirror or another shintai houses the kami and is never displayed. A crown announces a ruler to onlookers; a mirror kept in a box behind a curtain announces nothing, because its function is towards the deity, not the audience. The consequence is a regalia set no member of the public has seen, which the wider symbol traditions around royal objects make look very strange indeed.
Is Jimmu's eastward campaign history?
The chronicles date it with a precision that is itself the giveaway — 660 BCE, a year generated by applying a Chinese sixty-year cycle arithmetic backwards to produce an auspicious starting point, and centuries earlier than any archaeology supports for a unified polity. The campaign narrative, with its detours, battles and omens, has the texture of consolidated regional legend rather than record. What historians take seriously is the underlying direction of travel: cultural and political currents did run from northern Kyushu towards the Kinai region, and Kyushu was the point of contact with the continent. The Japanese family tree marks where the chronicles' mythological generations give way to their legendary ones, and the tradition overview explains why the boundary is impossible to draw sharply.