Japan sent its economic revitalisation minister Ryosei Akazawa to kick start the talks, expecting to face Trump's Treasury Secretary Scott Bessent in Washington DC and had hoped to limit the scope of discussions to trade and investment matters.
But Trump weighed in early on Wednesday, saying he would also be there to cover issues including the amount Japan pays towards the cost of hosting US troops in Japan, the biggest overseas deployment globally.
"Japan is coming in today to negotiate Tariffs, the cost of military support, and 'TRADE FAIRNESS'," he said in a post on Truth Social.
"I will attend the meeting, along with Treasury & Commerce Secretaries. Hopefully something can be worked out which is good (GREAT!) for Japan and the USA!"
Bessent also wants to discuss the thorny issue of exchange rates with Japan, one of the first countries to begin face-to-face negotiations since Trump announced sweeping duties on dozens of countries - both friend and foe - earlier this month.
Japan has been hit with 24 per cent levies on its exports to the United States although these rates have, like most of Trump's tariffs, been paused for 90 days.
But a 10 per cent universal rate remains in place as does a 25 per cent duty for cars, a mainstay of Japan's export-reliant economy.
Bessent has said there is a "first mover advantage" given the United States has said more than 75 countries have requested talks.
However, Japanese Prime Minister Shigeru Ishiba said on Monday that his country, a close US ally, won't rush to reach a deal and does not plan to make big concessions.
Ishiba has, for now, ruled out countermeasures to the US tariffs.
"The difficulty for the Japanese team is that the United States has created a huge amount of leverage for itself, unilaterally," said Kurt Tong, managing partner at The Asia Group, a US-based consultancy.
"The US is offering to not hit Japan with sticks, and Japan is stuck in a position of offering a whole lot of carrots. And from their perspective, it feels like economic coercion," said Tong, a former US State Department official.
Trump has long complained about the US trade deficit with Japan and other countries, saying US businesses have been disadvantaged by trade practices and intentional efforts by other countries to maintain weak currencies.
Japan denies it manipulates its yen currency to gain advantage.
Bessent met Vietnam's deputy prime minister last week to discuss trade and has invited South Korea's finance minister for talks next week.
Italian Prime Minister Giorgia Meloni will meet Trump at the White House on Thursday to discuss tariffs imposed on the European Union.
The full scope of Wednesday's discussions was not yet clear.
Bessent has said he is hoping to strike deals that would cover tariffs, non-tariff barriers and exchange rates although Japan had lobbied to keep the latter separate.
Possible Japanese investment in a multi-billion dollar gas project in Alaska could also feature, Bessent has said.
Japan hopes that pledges to expand investment in the United States will help to convince the US that the two countries can achieve a "win-win" situation without tariffs, Akazawa said ahead of his departure.
