On May 1, Crown Prince Naruhito will ascend to the throne of chrysanthemum after his father abdicated, becoming the new emperor of Japan.
Both the abdication and the adhesion will involve profoundly symbolic Shinto ceremonies, and in the center of them there will be three objects – a mirror, a sword and a gem – known as the Imperial Treasures or Regalia.
The origins and the place where the mysterious objects are located are wrapped in secrecy, but the myths about them are scattered throughout Japanese pop history and culture.
Why are imperial treasures so important?
The unofficial national religion of Japan, Shinto, attributes an enormous importance to the ritual to maintain a link with the past and with the spirits that intervene in human lives.
Imperial treasures are part of this. They are said to have been handed down by the gods through generations of emperors seen as their direct descendants. In the absence of an imperial crown, the treasures serve as a symbol of imperial power.
But the treasures are so sacred, they are kept hidden from the world.
"We don't know when they were made, we never saw them," Professor Hideya Kawanishi of Nagoya University told the BBC.
"Even the Emperor never saw them."
In reality they will not even be crowned – the replicas (which still won't be seen) will be used, and the originals – if they are too – will remain in their sanctuaries throughout the country.
Yata no Kagami: the sacred mirror
It is believed that the mirror, which could be over 1,000 years old, is preserved in the great shrine of Ise, in the prefecture of Mie. According to Shinsuke Takenaka at the Institute of Moralogy – a Japanese body that researches ethics and morality – it is considered the most precious of treasures.
It was the only treasure that did not appear in the last enthronement of 1989.
In Japanese folklore, mirrors are said to have divine power and reveal the truth. In imperial ceremonies, Yata no Kagami – or eight-sided mirror – represents the wisdom of the emperor.
According to the Kojiki, the ancient written testimony of Japanese legends, the Yata no Kagami was created by the deity Ishikoridome.
After the sun goddess Amaterasu fought with her brother Susanoo, the god of the sea and storms, she retreated into a cave bringing with her the light of the world.
Susanoo organized a party to attract her, and Amaterasu was dazzled by his reflection in the mirror. They repaired their quarrel, bringing the light back into the universe.
The mirror and other treasures ended up reaching Amaterasu's nephew, Ninigi.
According to legends, says Takenaka, the goddess said to Ninigi: "Serve this mirror as my soul, just as you would use me, with a clean mind and body".
Ninigi is believed to be Jimmu's great-grandfather, who according to legend became the first emperor of Japan in 660 BC.
Kusanagi no Tsurugi – the sacred sword
The position of the Kusanagi no Tsurugi – or lawn mower – is not clear, but could be at the Atsuta Shrine in Nagoya.
The legend says that it grew in the tail of an eight-headed snake that devoured the daughters of a wealthy family.
The father asked Susanoo for help, promising the marriage with his last uneaten daughter, if he could get rid of the snake. Susanoo deceived the snake to get drunk, then cut off the tail, finding the sword.
But he didn't do it long – this was also used in his efforts to recover with his sister, Amaterasu.
The sword represents the courage of the emperor. Because so little is known about it and where it is kept, some wonder if the sword still exists.
Certainly it was kept secret – a priest who reported seeing him in the Edo period (sometime between the 17th and 19th centuries) was banned.
There are rumors that they may have been lost at sea during a battle of the twelfth century, but Mr. Takenaka says it may have been a copy, and that a duplicate of the one, kept in the palace, is used for coronations.
When the emperor Akihito ascended the throne in 1989 he was assigned a sword that was said to be Kusanagi no Tsurugi. But the box that was given to him remained closed.
Yasakani no Magatama: the sacred jewel
A magatama is a type of curved bead that began to be produced in Japan around 1000 BC. Originally decorative, they began to take on a symbolic value.
According to legend, the Yasakani no Magatama was part of the necklace made by Ame-no-Uzume, goddess of joy, who played a central role in efforts to attract Amaterasu from her cave.
He performed an extravagant dance, wearing beads, to cause emotion and attract the attention of the sun goddess.
Whatever its origins, the Yasakani no Magatama, made of green jade, could be the only "original" that survived among the three treasures.
It is housed in the Tokyo Imperial Palace and in the enthronement ceremony, it represents the kindness requested of an emperor.
Do the Japanese believe in treasure?
While the emperors of Japan track their descent from Amaterasu, they no longer claim to be gods: the emperor Hirohito renounced his divine status after Japan's defeat in World War II.
Professor Kawanishi says that in Japan there are many who still think that objects are imbued with divine power, but that many people "think of them now more as ornaments, a bit like a crown in other monarchies".
They are largely important because "they show the mystery of the emperor", he says, and as "a symbol that the system has continued for a long time".
Takenaka states that among scholars there is also a view that objects represent the fusion of Japan's ancient indigenous groups with newcomers.
Based on this theory, he says, the three treasures are a symbol that the emperor should unite ethnic groups without discrimination.
But he adds that in the 20th century the term "three treasures" has taken on a slightly more practical meaning, becoming the phrase for the three things that the Japanese felt they could not live without: a TV, a refrigerator and a washing machine .
Additional reporting by Mariko Oi