We were never friends: A massacre on the eve of WW2 still haunts China-Japan relations

Japanese vlogger Hayato Katos 1.9 million followers are used to his funny clips about exploring China, where he has been living for several years.

But on 26 July he surprised them with a sombre one.

"I just watched a movie about the Nanjing Massacre," he said, referring to the Japanese armys six-week rampage through Nanjing in late 1937, which, by some estimates, killed more than 300,000 civilians and Chinese soldiers. Around 20,000 women were reportedly raped.

Dead To Rights, or Nanjing Photo Studio, is a star-studded tale about a group of civilians who hide from Japanese troops in a photo studio. Already a box office hit, it is the first of a wave of Chinese movies about the horrors of Japanese occupation that are being released to mark the 80th anniversary of the end of World War Two. But a sense of unfinished history - often amplified by Beijing – persists, fuelling both memory and anger.

Speaking in Chinese on Douyin, Chinas domestic version of TikTok, Kato recounted scenes from the film: "People were lined up along the river and then the shootings began… A baby, the same age as my daughter, was crying in her mothers arms. A Japanese soldier rushed forward, grabbed her, and smashed her into the ground."

He said he had seen many people on the Japanese internet denying the Nanjing Massacre had happened, including public figures, even politicians. "If we deny it, this will happen again," he continued, urging Japanese people to watch the movies and "Iearn about the dark side of their history".

The video quickly became one of his most popular, with more than 670,000 likes in just two weeks.

But the comments are less positive. The top-liked one quotes what has already become an iconic line from the movie, uttered by a Chinese civilian to a Japanese soldier: "We are not friends. We never were."

For China, Japans brutal military campaign and occupation are among the darkest chapters of its past – and the massacre in Nanjing, then the capital, an even deeper wound.

What has made it fester is the belief that Japan has never fully owned up to its atrocities in places it occupied – not just China, but also Korea, what was then Malaya, Philippines, Indonesia. One of the most painful points of contention involves "comfort women" - the approximately 200,000 women who were raped and forced to work in Japanese military brothels. To this day, the survivors are still fighting for an apology and compensation.

In his video, Kato seems to acknowledge that its not a subject of conversation in Japan: "Unfortunately these anti-Japanese war movies are not shown in Japan publicly, and Japanese people are not interested to watch them."

When the Japanese Emperor announced on 15 August that he would surrender, his country had already paid a terrible cost – more than 100,000 had been killed in bombing raids on Tokyo, before two atom bombs devastated Hiroshima and Nagasaki.

Japans defeat, however, was welcomed in large parts of Asia, where the Imperial Japanese Army had claimed million of lives. For them, 15 August carries both freedom and lingering trauma – in Korea the day is called gwangbokjeol, which translates to the return of light.

"While the military war has ended, the history war continues," says Professor Gi-Wook Shin, of Stanford University, explaining the two sides remember those years differently, and those differences add to the tension. While the Chinese see Japanese aggression as a defining, and devastating, moment in their past, Japanese history focuses on its own victimhood - the destruction caused by the atom bombs and post-war recovery.

"People I know in Japan dont really talk about it," says a Chinese man who has been living in Japan for 15 years, and wished to remain anonymous.

"They see it as something in the past, and the country doesnt really commemorate it - because they also view themselves as victims."

He calls himself a patriot, but he says that hasnt made things difficult for him personally because their reluctance to talk about it means they "avoid such sensitive topics".

"Some believe the Japanese army went to help China build a new order - with conflicts occurring in that process. Of course, there are also those who acknowledge that it was, in fact, an invasion."

China fought Japan for eight years, from Manchuria in the north-east to Chongqing in the south-west. Estimates of those killed range from 10 to 20 million. The Japanese government says around 480,000 of its soldiers died in that time.

Those years have been well-documented in award-winning literature and films – they were also the subject of Nobel laureate Mo Yans work.

That period is now being revisited under a regime that holds patriotism as central to its ambitions: "national rejuvenation" is how Xi Jinping describes his Chinese dream. While the Party heavily censors its own history, from the Tiananmen Square massacre to more recent crackdowns, it encourages remembering a more distant past – with an outside enemy.

Xi even revised the date the war with Japan started – the Chinese government now counts the first incursions into Manchuria in 1931, which makes it a 14-year war, rather than eight years of full-fledged conflict.

Under him, Beijing has also been commemorating the end of World War Two on a bigger scale. On 3 September, the day Japan formally surrendered, there will be a major military parade in Tiananmen Square.

Also in September, a highly-anticipated new release will focus on the notorious Unit 731, a branch of the Japanese Army that conducted lethal human experiments in occupied Manchuria. The date of release – 18 September – is the day Japan attempted its first invasion of Manchuria.

That is apart from Dongji Rescue, a film inspired by the real-life efforts of Chinese fishermen who saved hundreds of British prisoners of war during Japanese raids; and Mountains and Rivers Bearing Witness, a documentary from a state-owned studio about Chinese resistance.

And they seem to be striking a nerve.

"That one generation fought a war on behalf of three, and endured suffering for three. Salute to the martyrs," a popular RedNote post on Nanjing Photo Studio reads.

"We are not friends...", the now-famous line from the movie, "is not just a line" between the two main characters, says a popular review that has been liked by more than 10,000 users on Weibo.

It is "also from millions of ordinary Chinese people to Japan. Theyve never issued a sincere apology, they are still worshipping [the war criminals], they are rewriting history – no-one will treat them as friends", the comment says, referring to some Japanese right-wing figures dismissive remarks.

Tokyo has issued apologies, but many Chinese people believe they are not profuse enough.

"Japan keeps sending a conflicting message," Prof Shin says, referring to instances where leaders have contradicted each other in their statements on Japans wartime history.

For years, in Chinese history classes, students have been shown a photo of former West German Chancellor Willy Brandt kneeling before a memorial to the Warsaw Ghetto Uprising in 1970. The Chinese expect a similar gesture from Japan.

This wasnt always the case, though.

When Japan surrendered in 1945, the turbulence in China did not end. For the next three years, the Nationalist Kuomintang – then the ruling government and the main source of Chinese resistance against Japan – fought a civil war against Mao Zedongs Communist Party forces.

That war ended with Maos victory and the Kuomintangs retreat to Taiwan. Mao, whose priority was to build a communist nation, avoided focusing on Japanese war crimes. Commemorations celebrated the Partys victory and criticised the Kuomintang. He also needed Japans support on the international stage. Tokyo, in fact, was one of the first major powers to recognise his regime.

It wasnt until the 1980s - after Maos death - that the Japanese occupation returned to haunt the relationship between Beijing and Tokyo. By then, Japan was a wealthy Western ally with a booming economy. Revisions to Japanese textbooks began to spark controversy, with China and South Korea accusing Japan of whitewashing its wartime atrocities. China had just begun to open up, and South Korea was in transition from military rule to democracy.

As Chinese leaders moved away from Mao – and his destructive legacy – the trauma of what happened under Japanese attack became a unifying narrative for the Communist Party, says Yinan He, associate professor of international relations at Lehigh University in the US.

"After the Cultural Revolution, Chinese people for the large part were disillusioned by communism," she told the BBC. "Since communism lost its appeal, you need nationalism. And Japan is [an] easy target because thats the most recent external [aggressor]."

She describes a "choreographed representation of the past", where commemorations of 1945 often downplay the contributions of the US and the Kuomintang, and are accompanied by growing scrutiny of Japans official stance on its wartime actions.

What hasnt helped is the denial of war crimes - prominent right-wing Japanese dont accept the Nanjing massacre ever happened, or that Japanese soldiers forced so many women into sexual slavery - and recent visits by officials to the Yasukuni Shrine, which honours Japans war dead, including convicted war criminals.

This hostility between China and Japan has spilled over into everyday lives as nationalism online peaks - Chinese and Japanese people have been attacked in each others countries. A Japanese schoolboy was killed in Shenzhen last year.

Chinas economic rise and assertiveness in the region and beyond has changed the dynamic between the two countries again. It has surpassed Japan as a global power. The best time to seek closure – the 1970s, when the countries were closer - has passed, Prof He says.

"They simply said, lets forget about that, lets set that aside. Theyve never dealt with the history – and now the problem has come back to haunt them again."