The leaders of Japan, China and South Korea will sit down for three-way talks on Wednesday for the first time in 2½ years, with North Korea and economic cooperation set to be high on the agenda.
Ties have been fraught in recent years, in part due to territorial disputes and Chinese mistrust of American overreach on its two allies.
The summit in Tokyo comes amid warmer diplomatic relations between the three nations, catalysed by an apparent detente on the Korean peninsula and growing concerns over trade protectionism.
It is Japan's turn to host the summit, which was meant to be an annual affair, but has not been held since the last round in Seoul in 2015.
It will be the first visit to Japan for Chinese Premier Li Keqiang and South Korean President Moon Jae In since they took office. This year marks the 40th anniversary of the signing of a friendship treaty between Beijing and Tokyo. Japanese Prime Minister Shinzo Abe will also hold bilateral talks with Mr Li and Mr Moon on the sidelines.
The three nations are expected to issue a joint statement to pledge trilateral cooperation towards the denuclearisation of the Korean peninsula - but are still in disagreement on how the document should be worded, Japanese sources told the Nikkei Asian Review last Saturday.
This is because, the Nikkei reported, they differ on how to proceed with North Korean leader Kim Jong Un's vow for "complete denuclearisation" as stipulated in the Panmunjom Declaration, released after the historic summit with Mr Moon last month.
South Korea prefers a statement that says "the three leaders fully accept the Panmunjom Declaration as it is", Presidential Blue House spokesman Kim Eui Kyeom told reporters last week. "So, there is no reason for it to include support for 'complete, verifiable and irreversible' dismantlement of the North Korean nuclear programme."
But it is understood that Japan prefers an explicit mention of a "comprehensive" resolution.
The Nikkei said that China is open towards incremental rewards such as the provision of economic assistance in exchange for phased denuclearisation - which is at odds with Japan's stance to continue maintaining maximum pressure.
Dr Jin Chang Soo, president of South Korean think-tank Sejong Institute, told The Straits Times that Mr Moon may "present a road map for Japan and China to play a role in the inter-Korea peace agreement".
Yet questions about US military presence on the Korean peninsula may also arise during summit talks, amid speculative reports that Washington is considering scaling down the size of its troops.
Dr Takashi Suzuki of Japan's Aichi Prefectural University told The Straits Times that with the potential opening up of the North, "Japan is afraid that the Korean peninsula will become an arena of 'Great Games' confrontation as the US, China and Russia each exercise more explicit influence and power".
Dr Chung Jae Hung from Sejong Institute said: "It's like opening a Pandora's box. China is always sensitive and attentive to changes in US forces in South Korea...
"If a peace regime is established, China will question the nature, role, strategic meaning and relevance of US troops here."
Amid rising protectionism, the three nations will stress the role of free trade in Asian prosperity, and pledge to speed up efforts towards a trilateral agreement that has been in the works since 2012. According to World Bank estimates, the three nations together account for 22.6 per cent of the global economy.
They will also agree to accelerate efforts on the Asean-led, 16-country Regional Comprehensive Economic Partnership deal that also involves Australia, India and New Zealand.
Professor Zhou Yongsheng of China Foreign Affairs University said: "China will focus on pushing for the deepening of economic cooperation among the three countries, expanding the areas of cooperation so that eventually, the free trade pact could be signed."
• Additional reporting by Chong Koh Ping in Shanghai and Chang May Choon in Seoul