Historical grievances and territorial disputes have added to the strain.

AFP examines the issues at the heart of their complicated relationship.

- Historical mistrust -

Japanese troops carried out mass murder, rape and looting in Nanjing for about six weeks from the end of 1937, a period of brutal Japanese occupation in the Second Sino-Japanese war that was part of World War II.

Tens, if not hundreds, of thousands of people were killed in the massacre.

Tokyo normalised diplomatic ties with Beijing in 1972 but relations are still dogged by historical issues.

More than 10,000 people protested in Beijing after Tokyo approved revisionist textbooks in 2005, hurling rocks and eggs at the Japanese embassy.

Takaichi has not commented publicly on the Nanjing massacre since becoming premier last month, but she questioned the official Chinese death toll of 300,000 in a 2004 blog.

Long seen as a China hawk, she has also been a regular visitor to a shrine that honours Japan's war dead -- including those guilty of crimes in World War II -- although she has not visited since taking over.

China terms such visits as "serious provocations".

- Territorial disputes -

The East Asian neighbours have also been involved in a territorial dispute over islets in the East China Sea, known by Tokyo as Senkaku and by Beijing as the Diaoyu.

The remote chain of islands has long fuelled tensions and is the scene of regular confrontations between Japanese coast guard vessels and Chinese fishing boats.

Beijing has grown more assertive about its claim over the islands in recent years, with Tokyo reporting the presence of Chinese coast guard vessels, a naval ship and even a nuclear-powered submarine.

Chinese coast guard vessels spent several hours in Japan's territorial waters around the Senkakus on Sunday, according to Japan's Chief Cabinet Secretary Minoru Kihara.

Separately, two Chinese aircraft carriers were seen operating in the Pacific for the first time this year, with Japan saying the move revealed an expansion of Beijing's military activities.

- Alliances -

The United States has been a staunch ally of Japan since the end of World War II and Takaichi vowed a "new golden age" of ties with Washington during President Donald Trump's visit to Tokyo last month.

Japan hosts several US military bases, with the bulk of the 60,000-strong troop presence in the southernmost region of Okinawa -- right on mainland China's doorstep.

That has fuelled China's belief that the United States is intent on encircling and containing it.

Tensions between China and other claimants to parts of the East and South China Seas have also pushed Japan to deepen ties with the Philippines.

Their coast guards held training drills with the United States in Japan for the first time this year.

- Taiwan -

Another flashpoint issue is Taiwan -- which Beijing claims as its territory and has vowed to take one day, by force if necessary.

Takaichi suggested this month that Japan could intervene militarily in any emergency in the self-ruled island, sparking a row during which a Chinese diplomat in Japan threatened to "cut off that dirty neck" in an apparent reference to her.

China and Japan summoned each other's ambassadors last week, with Beijing then warning its citizens to avoid travelling to Japan and saying the safety of Chinese students there was at risk.

Japan said on Monday it had scrambled fighter jets when a suspected Chinese drone was detected nears its southern island of Yonaguni, which is close to Taiwan, two days earlier.

China has staged war games around Taiwan, which was ruled by Japan for half a century until 1945, several times since 2022.

- Trade and tourism -

Asia's two biggest economies are still closely entwined, with China being Japan's largest trading partner and one of the biggest investment destinations for Japanese companies.

The neighbours maintain several hundred billion dollars in economic trade annually.

China is also the biggest source of tourists to Japan, with almost 7.5 million in the first nine months of 2025, according to the Japanese figures.

Chinese tourists spent 590 billion yen ($3.8 billion) in the third quarter, accounting for about 28 percent of all spending by international tourists, transport ministry data showed.