US President Barack Obama walks with Japan's Emperor Akihito and Empress Michiko during a welcoming ceremony at the Imperial Palace in Tokyo on April 24, 2014. - AFP
Tokyo (AFP) - Barack Obama inspected the guard at a pomp-filled ceremony with Emperor Akihito Thursday, kicking off the formal proceedings of the first state visit to Japan by a US president in nearly two decades, at a time of nervousness in Asia.
In the grounds of Tokyo's sprawling Imperial Palace, Obama strode in bright spring sunshine as he greeted a line of dignitaries.
Soon after he arrived in Japan on Wednesday night, Obama's presidential motorcade whisked him to a tiny underground sushi restaurant, where he feasted on three Michelin star food with Japanese Prime Minister Shinzo Abe.
He emerged from the restaurant to declare to a crowd of journalists and well-wishers: "That's some good sushi right there".
Japanese media, citing a restaurant employee in the same building as the eatery, said Obama and Abe -- who were not wearing ties at what was billed as an informal dinner -- had begun intensive discussions almost as soon as they sat down.
Thursday's ceremony was to be followed by a formal summit with Abe, and then a tour of Meiji Jingu shrine, a popular tourist spot. A full state dinner was planned for the evening.
The grandness of the occasion is very important to Japan, which is looking for reassurances that the US will stand by it in a corrosive row with China over the sovereignty of a small chain of islands in the East China Sea.
Ahead of his arrival, Obama had made clear the US would support Tokyo if China took any hostile action over the archipelago.
In an interview with Yomiuri Shimbun newspaper, he said the US would oppose any "unilateral attempts to undermine Japan's administration" of the Senkaku Islands, which Beijing claims as the Diaoyus.
"The policy of the United States is clear -- the Senkaku Islands are administered by Japan and therefore fall within the scope of Article 5 of the US-Japan Treaty of Mutual Cooperation and Security," he said in the article.
In many ways, Abe is the kind of dynamic leader that Washington, frustrated by years of stagnation in Japanese politics and the economy, had longed for.
But his nationalistic impulses and ritual offerings to a shrine that counts senior war criminals among the fallen warriors it honours bring headaches for Washington, and complicate Japan's relations with China and South Korea.
- Discussions on key trade partnership -
Obama plans to flesh out his vision for his "rebalancing" strategy, and ease consternation in Japan about what exactly Washington and Beijing intend when they talk of a new "great power" relationship.
The two leaders are also under pressure to make progress on auto and agricultural market access issues blocking agreement on the wider Trans-Pacific Partnership (TPP) -- a proposed 12 nation trade bloc.
Top negotiators from both sides have spent days seeking a breakthrough over the dispute, which will entail painful political choices which could inflame anti-free trade advocates in both Japan and the United States.
Senior US officials and business figures acknowledge progress is critical to hopes of concluding the TPP, a vital prong of Obama's Asia pivot.
While Obama hopes to concentrate on Asia policy on a trip partly making up for a cancelled visit to the region last year, he will find it tough to stick to his narrative as the Ukraine crisis deepens.
Washington is on the cusp of stiffening sanctions on Russia following the apparent failure of an agreement reached with Moscow in Geneva last week to de-escalate tensions in eastern Ukraine.
Time spent on the worst East-West clash since the Cold War as Obama travels through Asia would be an apt metaphor.
Obama's attention has repeatedly been wrenched away from the region by global crises elsewhere during his presidency, leading some Asian allies to question US endurance in the region.
His trip will also take him to South Korea, Malaysia and the Philippines.
Efforts to curb North Korea's nuclear ambitions will be a key topic in Seoul, and the US leader will also offer condolences for a ferry disaster feared to have killed hundreds.