Japan is one of the closest allies of the United States in Asia with around 54,000 US military personnel stationed in the country.

Ishiba will be pushing for reassurance on the importance of the US-Japan alliance, as Trump's "America First" agenda risks encroaching on the nations' trade and defence ties.

"It would be wonderful if we could affirm that we will work together for the development this region and the world and for peace," Ishiba told reporters in Tokyo before leaving for the trip.

Japan's Nikkei newspaper said Thursday the pair will issue a joint statement, which could vow to build a "golden age" of bilateral relations and bring the alliance to "new heights".

Ishiba is expected to tell Trump that Japan will increase defence purchases from the United States, the Nikkei said.

Ishiba may also propose importing more US natural gas -- chiming with Trump's plan to "drill, baby, drill" while boosting energy security for resource-poor Japan.

Since Japan has cut its liquefied natural gas (LNG) imports from Russia, it "desperately needs to open up new sources of LNG, and other energy more broadly", Sheila Smith, senior fellow at the Council on Foreign Relations, told AFP.

"The intention is to present a win-win value proposition from Ishiba to the president," she said.

Trump will meet Ishiba in Washington on Friday -- just days after a joint press conference with Israeli Prime Minister Benjamin Netanyahu, where the US president sparked uproar with a proposal to take over the Gaza Strip.

The Japan summit could be less startling, Smith said, as Trump "has a fairly strong commitment to the alliances in Asia".

- Taiwan threat -

Ishiba has stressed the importance of US defence ties, pointing to threats on Japan's doorstep such as China pressing its claims of sovereignty on the self-ruled island of Taiwan.

Tokyo must "continue to secure the US commitment to the region, to avoid a power vacuum leading to regional instability", Ishiba recently told parliament.

Trump and Ishiba are expected to affirm the importance of peace and stability in the Taiwan Strait, Japanese media said.

That would echo joint statements made by the last US president Joe Biden with previous Japanese prime ministers.

Focusing on this point is "extremely important" because Japan and the United States must work together to prevent a potential crisis, said Takashi Shiraishi, an international relations expert at the Prefectural University of Kumamoto.

As Japan and the United States renegotiate how to share the burden of defence costs, however, there are concerns Trump could provide less cash and push Japan to do more, Smith said.

"That's where... the Ishiba-Trump relationship could get a bit sticky," she said.

- After Abe -

Also causing jitters is Trump's willingness to slap trade tariffs on major trading partners China, Canada, and Mexico -- though he has delayed measures against the latter two countries pending talks.

"I hope Ishiba will show him there are other ways to achieve economic security," such as cooperating on technology, Shiraishi told AFP.

One example is the Stargate drive, announced after Trump's January inauguration, to invest up to $500 billion in AI infrastructure in the United States, led by Japanese tech investment behemoth SoftBank Group and US firm OpenAI.

Reports said the leaders could also discuss Nippon Steel's $14.9 billion bid to buy US Steel, which Biden blocked on national security grounds.

Japan and the United States are each other's top foreign investors, and the Nikkei reported that the leaders will agree on creating an investment-friendly environment.

During his first term, Trump and Japan's then-prime minister Shinzo Abe enjoyed warm relations.

As president-elect in December, Trump also hosted Akie Abe, the widow of Japan's assassinated ex-premier, for a dinner with Melania Trump at their Florida residence.

Trump built a strong relationship with Abe, for whom Smith believes he had a "genuine fondness".

He will likely "see Ishiba through a different lens", said Smith, and "it will be more the state-to-state relationship, not the personal".

Ishiba, 68, will not be the first Japanese VIP to meet the 78-year-old Trump in person since he took office -- a distinction held by SoftBank founder Masayoshi Son.