Tokyo: Japanese officials are wary ahead of the arrival of outspoken Philippine President Rodrigo Duterte. It’s not just his foreign policy toward the US, but also his informal style: Will he chew gum in front of the emperor?

Duterte arrives in Tokyo later Tuesday for a three-day visit, his first as Philippine leader.

For diplomats and political leaders, the main issue is Duterte’s foreign policy toward Washington and how Japan can help mend those ties.

Tokyo is a major ally of the United States, and has watched as Duterte increasingly attacked the US and said he would scale back America’s military engagement with his country. And he has worried Japan and the United States by reaching out to China.

Japanese Foreign Minister Fumio Kishida acknowledged Duterte’s remarks have triggered concern, and told reporters he planned to ask what his real intentions were when the two have dinner Tuesday. He said Prime Minister Shinzo Abe will do the same on Wednesday.

“I think it would be important that we fully communicate through these occasions and directly hear opinions from President Duterte himself,” Kishida said.

In a country where formality and politeness are highly valued, others in Japan are worried about the rough side of Duterte’s manners. They are particularly concerned about his meeting with Emperor Akihito on Friday.

Japanese TV shows have repeatedly shown Duterte apparently chewing gum — at meetings, shaking hands and at other public occasions. In footage of a meeting with Chinese President Xi Jinping, Duterte wore a business suit instead of a formal Philippine “Barong” shirt. He walked in with his hands in his pockets and chewed gum during the hand shake and a signing ceremony.

Duterte doesn’t usually button up the top of his shirt, often wears slacks or jeans and has been seen without socks.

“When (Duterte) will make a courtesy visit to the Emperor, his behaviour during the event could have a major impact. I trust he understands the consequences and he would not do such a thing (as chewing gum), but I do hope the Philippine side to remind him of that particular point,” Itsunori Onodera, a senior lawmaker in the conservative ruling Liberal Democratic Party, told a Sunday talk show on Fuji TV.

In Japan, where the Emperor was considered a living god until the end of World War II, people are expected to be extra polite in front of him and his family.

“It’s unbelievable. I have never seen anything like that!” said Kunihiko Miyake, a former diplomat and political analyst. “How could he dare to behave in ways that could cause his host to lose face.” Miyake, however, said Duterte might have done so intentionally perhaps because he was unhappy about compromising on the South China Sea issue.

While serving as a mediator between the two allies, Japan’s main contribution to Manila is likely to be two large Coast Guard patrol boats — in addition to an earlier pledge of 10 smaller ones — and TC-90 military training aircraft to help boost the Philippine’s maritime security in the South China Sea.