TOKYO >> Japanese Emperor Naruhito will perform a secretive and controversial ritual Thursday, a once-in-a-reign event to give thanks for good harvests, pray for the peace and safety of the nation and play host to his family’s ancestral gods.

Or at least that’s what experts and officials say.

The Daijosai, or great thanksgiving festival, is the most important succession ritual an emperor performs. But it is closed to the public, even as taxpayer money funds it.

It has drawn criticism as a throwback to Japan’s authoritarian past and as a colossal waste of money, and provoked speculation the emperor is spending the night on a bed with a goddess.

Here’s a look at the significance of the ritual and what people are saying about it:

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FIRST COMMUNION WITH GODS

Daijosai marks the emperor’s first communion with the Sun Goddess Amaterasu, the monarchy’s mythological ancestor, and with other gods of Shinto, the religion of the imperial family. Harvest rituals originated in Japan’s ancient rice growing culture from around the 7th century, historians say.

The two-part ritual, each one lasting a few hours, begins Thursday evening. Naruhito, after purifying himself and donning a white robe, will enter the Yukiden, one of two main halls at a newly prepared, and very expensive, shrine complex inside his palace. Only he can enter the innermost sanctum to present harvested rice, sake, vegetables, seafood and local produce from around the country to the goddess and gods.

Naruhito will offer arcane prayers for peace and bountiful harvests, then partake of the offerings in a symbolic communion. After a short break, he will perform the other ritual at another main hall, the Sukiden.

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ONE NIGHT, $18 MILLION SHRINE

The venue, Daijokyu, is a one-off shrine complex of about 30 structures in various sizes, including the two main halls, all of which will be demolished afterward. The shrine complex alone costs about 2 billion yen ($18 million), and the whole ritual will total 2.9 billion yen ($27 million).

It’s all funded by the government.

The ritual shrank when Japan was ruled by warlords and the monarchy had little money and power. There was a 200-year hiatus before it was restored during the Tokugawa shogunate, which ruled from the 17th to the 19th century.

The ritual and the shrine were expanded when the pre-World War II government deified the emperor and used his status to drive Japanese aggression. The event has not been scaled down even after the emperor became a mere symbol, with no political power, under the postwar constitution, and there’s been little public debate about the use of taxpayer money for the highly religious and secretive event.

Keiko Hongo, a University of Tokyo historian who was invited to speak before a government committee on the ritual, said officials wanted to cut costs of other events but not the Daijosai.

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WHAT’S THE BED FOR?

There’s speculation about many aspects of the ritual, but especially about the presence of a bed in the main hall, and what it might be used for.

Some experts believe the emperor uses it to sleep with the sun goddess to gain divinity. Others say it’s for the goddess to rest and that it’s not even touched by the emperor.

“The so-called bed, as we understand it, is a sacred seat for the imperial ancestor to rest,” then-Prime Minister Toshiki Kaifu said before the Daijosai in 1990 was performed by former Emperor Akihito, the current emperor’s father.

Officials have denied that the emperor uses the bed to gain divinity.

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RELIGION AND STATE

The government’s funding of the highly religious rite remains contentious.

A group of more than 200 people filed a lawsuit against the government last year, saying the ritual violates the constitutional separation of state and religion. The wartime government turned Shinto into a fascist ideology to promote its colonial aggression.

Abe’s government says even though the rite is too religious to be considered an official duty of the emperor, it is an “extremely important” succession ritual for the country’s hereditary monarchy written in the constitution and therefore it serves the public interest and deserves state funding. The cost is paid in the name of “palace expenses,” which ordinarily cover maintenance and ceremonial spending by the palace, following a precedent set by the government at the time of the earlier event.

“There seems to be a political intention to resist (calls to stop funding the ritual) because of a sense of nostalgia for the (prewar) era,” Takeshi Hara, a monarchy expert at the Open University of Japan, told a TBS radio talk show this week.

Abe’s government wants the emperor to be a more authoritative figure, as he was before the end of World War II.

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IMPERIAL CRITICISM

Naruhito’s younger brother, Crown Prince Akishino, says he is against using public money for the ritual and that it’s questionable under a constitution that separates religion and state.

“It’s a royal family event, and it is highly religious,” Akishino said last year. The palace budget for the Imperial family’s private activities, including religious ones, was about one-seventh of the amount needed for the event. “I think the Daijosai should be held … by making it an affordable ceremony.”

His view was quickly dismissed by the government and conservatives, but widely welcomed by some palace watchers and legal experts. They say it’s doable because the emperor already performs a regular annual harvest ritual in November at the palace’s existing shrines.