President Trump meets with Japanese Prime Minister Shinzo Abe in the Oval Office on April 26. (Susan Walsh/AP)

In President Trump’s telling, the “very big event” in Japan is something he just can’t miss.

How big? “One hundred times bigger” than the Super Bowl, Trump boasted during an Oval Office meeting with Japanese Prime Minister Shinzo Abe last month.

“Something that hasn’t happened in over 200 years,” the president marveled this week, as he prepared to leave Washington for Tokyo on Friday.

What is happening? Trump hasn’t exactly said. He noted in remarks on Thursday that it has something to do with the emperor, but he hasn’t offered any details. “It’s a very big thing,” he assured reporters.

For Trump — who as a real estate developer and reality show star honed his talents for trumping up even the most modest of events to make them, and himself, seem larger — the hyping of his four-day trip to Japan has followed in a long line of boasts and pronouncements aimed at building up public anticipation for whatever he is working on.

The promoter in chief has touted dangerous hurricanes “as big as they’ve seen,” previewed plans for a revamped Independence Day fireworks display that would be “one of the biggest gatherings in the history of Washington, D.C.,” and told reporters in the White House briefing room to go to the West Wing driveway in March 2018 for a “major statement” on “the big subject” — his decision to meet North Korean leader Kim Jong Un.

But on the subject of Japan, Trump has been particularly vague. “It’s a very unusual thing,” he said during his meeting with Abe.

That “thing” is the crowning of Emperor Naruhito, who ascended this month after his father Akihito abdicated the throne — the first emperor to do so since 1817. Akihito, 85, had ruled for 30 years but chose to step down because of his age and health issues.

As he boasted about the importance of the event, Trump made no mention of either Naruhito or Akihito by name, nor of the new “Reiwa era” in Japan that marked Naruhito’s ascension. The royal succession is, indeed, a big deal in Japan, and the national celebration will last through a formal ceremony for Naruhito in October.

For Abe, the historic moment provided an opportunity to advance his tireless courting of Trump, once again playing to the president’s ego by inviting him to be the first foreign leader to meet Naruhito. Abe also is scheduled to escort Trump and first lady Melania Trump to the finale of the Grand Sumo tournament on Sunday, where they will be granted special chairs near the “dohyo,” or sumo ring. Trump plans to present a custom-made trophy nicknamed the “Trump Cup” to the winner.

Persuading Trump to make the trip was a bit tricky for Abe, who also was able to persuade Trump to return next month for the Group of 20 economic summit in Osaka. Trump told reporters during the meeting with Abe last month that he only agreed after Abe assured him the event was way bigger than the Super Bowl.

“I said, ‘I’ll be there. If that’s the case, I’ll be there,’ ” Trump said. He added: “Isn’t it 130-some-odd years that it’s happened? It’s a very unusual thing.”

Then he sort of alluded to something having to do with the emperor — “you’re talking about reigning through blood for over 3,000 years, the longest in the world” — before asking Abe to take over.

“It’s a very, very big event,” Trump said, “and maybe you could explain the event, because it’s very exciting, actually.”

Abe then explained the abdication of a “living emperor leading to the succession of the crown prince” for the “first time in approximately 200 years.”

Japanese officials in Washington said they have high hopes for Trump’s visit. During Trump’s first trip to Japan as president in November 2017, Abe played host to a banquet in his honor at which he invited golf legend Isao Aoki and pop star Pikotaro, whose song “Pen Pineapple Apple Pen” caught the fancy of Trump’s granddaughter Arabella three years ago. Trump used a toast to poke fun at Abe’s eagerness to meet with him after he won the election in 2016.

But this time, Trump will attend a state dinner presided over by Naruhito, and Japanese officials said they expect the event to be more serious and formal — a potential challenge for the impulsive president.

Yet if Abe’s goal was to use the emperor’s succession to flatter Trump in service of preserving the bilateral alliance, it appeared to be paying dividends. During an impromptu question-and-answer session with reporters in the Roosevelt Room on Thursday, Trump was asked whether the United States and Japan could reach a trade deal to avoid tariffs on Japanese automobiles that the president has threatened to enact in six months.

Instead of responding directly, Trump pivoted to boast again about the “very big thing going on with the emperor” and then, perhaps, revealed the real reason he is so enthusiastic.

“I am the guest, meaning the United States is the guest, but Prime Minister Abe said to me, very specifically, ‘You are the guest of honor. There’s only one guest of honor,’ ” Trump said. “I represent the country. Of all the countries in the world, I’m the guest of honor at the biggest event they’ve had in over 200 years.”