Abe later tweeted a selfie of the 2 grinning into the camera, as the pair relaxed before the formal element of Trump's 4-day trip begins on Monday with a visit to the new emperor and talks likely to touch on trade and North Korea. The United States and China are engaged in an expensive trade war that has pounded financial markets worldwide.
Later in the day, Abe was expected to introduce Trump to Japan's ancient sport of sumo wrestling.
In extensive face time with Trump - including a bilateral meeting and likely a round of golf - Abe hopes to stave off further trade tensions and gain assurances that the USA will remain tough on North Korea.
Trump, a fan and former promoter of the less tradition-bound WWE wrestling, entered the arena, stepped on to the dohyo ring and bowed at Asanoyama, a relatively unknown Japanese wrestler celebrating his first tournament victory.
"In honor of your outstanding achievement as sumo grand champion I hereby award you the President's Cup", Mr. Trump said.
The sumo crowd of 11,500 had been instructed to applaud the VIPs' arrival and warned not to hurl their seat cushions into the ring - a traditional show of appreciation for a particularly exciting bout or when a high-ranking wrestler suffers a shock defeat.
The two met early at a suburban golf course.
"I've always found that fascinating", Trump said about Japan's national sport during a meeting with Abe in Washington last month.
Some users made mean-spirited comments about photos of Melania Trump frowning during the sumo match.
"The relationship with Japan and the United States I can say for a fact has never been stronger, never been more powerful, never been closer", Trump said at the dinner.
Despite the bonhomie, trade was never far from mind.
"Great progress being made in our Trade Negotiations with Japan".
Mr Trump arrived shortly after a relatively strong natural disaster rattled Tokyo.
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The Japanese people will see the American president and their prime minister, Shinzo Abe, attend the final day of a 15-day sumo tournament on Sunday.
The prime minister caters to the president's preferences.
Sitting at the counter in front of a few dishes, Trump told the press they talked "a lot today about trade and military and various other things", describing the day as "very productive" and expressing confidence that would also be the case at their summit Monday.
Mr Trump recently agreed to a six-month delay, enough time to carry Mr Abe past July's Japanese parliamentary elections.
Beef was also heavily in play at lunch.
The president is threatening Japan with potentially devastating US tariffs on foreign autos and auto parts.
Mr Trump said on Saturday when he arrived in Japan: "With this deal we hope to address the trade imbalance, remove barriers to United States exports, and ensure fairness and reciprocity in our relationship".
He says: "I would say that Japan has had a substantial edge for many, many years, but that's OK. maybe that's why you like us so much".
"In the world of Donald Trump, bad things can happen if you're an ally, but no major blows have landed on Japan", said Michael Green, senior vice-president for Asia and Japan chair at the Center for Strategic and International Studies.
NPR's Ayesha Rascoe reports, "Japan wants to show it's the US best friend in the region, and this is important because Japan is dealing with China on the one hand, trying to assert its dominance, and North Korea on the other, being confrontational".
US officials have played down prospects of any major progress on the president's trip.
President Donald Trump is downplaying recent North Korean missile tests, tweeting from Tokyo that they're not a concern for him - even though they are for Japan.