U.S. President Donald Trump, who arrived in Tokyo on Saturday for a four-day state visit, will get down to business on Sunday with Prime Minister Shinzo Abe — by playing golf and watching sumo.

But, as strange as it may seem, these are serious diplomatic events for the two leaders, who have enjoyed a close personal relationship since Trump became president in January 2017.

Officials and experts have said the top priority for Trump's visit for both sides is to show off the two leaders' ties and highlight a strong Japan-U.S. alliance in the face of threats from China and North Korea.