TOKYO (NYTIMES) - When Mr Miki Dezaki decided to make a documentary for his graduate thesis, he examined a question that reverberates through Japanese politics: Why, 75 years later, does a small but vocal group of politically influential conservatives still fervently dispute internationally accepted accounts of Japan's wartime atrocities?

Specifically, Mr Dezaki focused on what historians call the Imperial Army's sexual enslavement of tens of thousands of Korean women and others in military brothels during World War II.

He explored in detail the conservatives' case that the so-called comfort women were in fact paid prostitutes.

Ultimately, Mr Dezaki was unpersuaded - he concluded that the conservatives were "revisionists" and used terms like "racism" and "sexism" to characterise some of their claims.

Now, five of them are suing him for defamation.

The conservatives whom he interviewed in the movie are part of a group that has influence at the highest levels of the Japanese government.

They have helped shape what Japanese children are taught, what works of art can be shown, and, perhaps most significantly, how Japan conducts important aspects of its foreign policy, most notably with South Korea.

Any reference to the women can raise the conservatives' ire. Last month, organisers of an international art fair in Nagoya closed an exhibition after receiving terrorist threats over a statue symbolising one of the Korean comfort women.

Mr Dezaki, his supporters and outside historians say the lawsuit over his film shows how nationalists seek to silence those who challenge them, while at the same time using any outlet they can to spread views that run counter even to an official 1993 Japanese government apology to the comfort women.

"The overarching theme of the film is, why do they want to erase this history?" 36-year-old Dezaki said.

The 1993 apology has been a festering wound for those on the political right, including Prime Minister Shinzo Abe, who have insisted that the Korean women were not sex slaves because there is no proof that they were physically forced into the brothels.

Diplomatic, economic and security ties between Japan and South Korea have reached their lowest point in years, a rupture that can be traced to the long-raging dispute over what Japan still owes for abuses committed during its colonial occupation of the Korean peninsula, including its treatment of the comfort women.

The conservatives have generally avoided the kind of reckoning that Germany has undergone in atoning for the Holocaust, as they argue that the actions of Japan during the war were no worse than those of other nations and should not damage national pride.

Many of the most vocal right-wing critics of the mainstream view of comfort women are older Japanese, but a younger cadre of social-media-savvy activists regularly pounce on those who describe the women as sex slaves.

"It is an issue that people get wild-eyed over," said Dr Jennifer Lind, an associate professor of government at Dartmouth College in New Hampshire and a specialist in Japanese war memory.

She said passions also run strong in South Korea, where activists accept no deviations from the narrative that the women were brutally enslaved.

In 2015, a court ordered a South Korean scholar to redact numerous passages from a book that suggested that the relationship between soldiers and the comfort women was more complex.

Mr Dezaki's two-hour documentary, Shusenjo: The Main Battleground Of The Comfort Women Issue, has been shown commercially in Japan and South Korea and will be shown on college campuses in the United States this autumn.

When he began his research, Mr Dezaki, a second-generation Japanese American who grew up in Florida and learnt little about the comfort women from his Japanese immigrant parents, said he wondered whether historical accounts in the Western news media "had got it wrong somehow".

To understand the mainstream view, he interviewed historians, advocates and lawyers who described their evidence.

Documents have proved the Japanese military's direct role in managing the brothels, and hundreds of women have described harrowing conditions in so-called comfort stations.

But the mainstream experts Mr Dezaki interviewed were also open about the lack of direct proof that the Japanese military physically abducted the women - a fact that the conservatives seize on - and forthright about the wide-ranging estimates of the numbers of women involved.

In the film, Mr Dezaki highlights a 1944 US Army document, cited by the conservatives, in which 20 Korean comfort women interviewed in Burma are described as "nothing more than" prostitutes who were "attached to the Japanese army for the benefit of the soldiers".

That same document says the women were recruited under "false pretences".

Mr Yoshiaki Yoshimi, a retired history professor who uncovered key documents describing the military's management of the brothels, said that by "denying one point", the conservatives "seek to deny the big picture".

Much of the film dwells on the nature of coercion.

In the end, Mr Dezaki said, he was convinced by the scholars who say the women were forced or deceived into providing sex to soldiers against their will.

In the movie, he concludes that to remember the comfort women is to fight "against racism, sexism and fascism".

"I did not defame them," Mr Dezaki said of the conservatives. "I made a film that documents the issue and the people involved."

He added: "Information is revealed in the film, and how the audience interprets this information is up to them."

But those suing Mr Dezaki say he is biased.

"'Revisionist' is a word with the greatest malice," said Mr Nobukatsu Fujioka, vice-president of the Japanese Society for History Textbook Reform, whose business card reads "Let's create Japanese who are proud!"

Another plaintiff, Mr Shunichi Fujiki, wrote in an e-mail, "I believe this is a fight to clarify who is the one fabricating history."

He added that in the United States, liberals "label conservatives as 'segregationists', 'KKK!', 'the Nazis!', 'Hitlers!', etc, but in actuality, the segregationists they're referring to are themselves."

Mr Kent Gilbert, an American lawyer and celebrity television commentator who has lived in Japan for more than 30 years, said that the film did not misrepresent his views but that it was "a propaganda hit piece".

The comfort women, he said, were just prostitutes.

"Everybody knows that," he said. "If you want to see prostitutes, look for the Koreans. My land, they've got prostitutes all over the world."

In addition to defamation, the lawsuit accuses Mr Dezaki and Tofoo Films, the distributor, of breach of contract, saying the plaintiffs agreed to be interviewed only for his graduate thesis, not a commercial film.

The plaintiffs are demanding compensation and a suspension of all public screenings.

All of the interviewees signed release forms giving Mr Dezaki full editorial control and copyright, said Mr Makoto Iwai, a lawyer who is representing Mr Dezaki and the film's distributor.

The New York Times reviewed two versions of the release.

Dr Koichi Nakano, a political scientist at Sophia University in Tokyo who was one of Mr Dezaki's professors and appears in the movie, said he believed that the plaintiffs were looking for a reason to bring a suit because the film's "interpretation doesn't fit entirely what they like".

Audiences in Japan and South Korea have said the film helped them understand the comfort women controversy in a new way.

At a showing in Seoul at Sogang University late last month, Ms Chae Min-jin, 26, said she "realised that we Koreans didn't really know the context and the logic in which the right-wingers in Japan asserted themselves after all".

In Japan, some audience members said the movie revealed information unavailable in their history textbooks.

Ms Tsubasa Hirose, a freelance copywriter, wrote on her movie-reviewing blog that she had always thought comfort women "treated people at the hospital, like nurses".

"I didn't know anything," she wrote, "and I wasn't given any opportunity to."

Mr Dezaki said he did not consider the debate closed.

"My conclusion is not final," he said. "I don't know everything. I feel like I can defend my conclusion based off what I know."

But, he added: "I'm always aware that there's a possibility that one of the factors in my argument might not hold."