Inside a windowless room at the Stone Street Studios in Wellington, a group of journalists are beginning to get on each other's nerves.

We're here because this is where Scarlett Johansson is filming the Hollywood adaptation of anime classic Ghost in the Shell. After almost 12 hours, we've inspected an array of sets – a concrete plaza, a burnt-out pagoda and dystopian streetscapes. We've seen racks of costumes for criminals, police and geishas (whose heads apparently explode in the sci-fi film's opening sequence). We've interviewed the cast of supporting actors. But the star of the show is nowhere to be found.

Johansson, Hollywood royalty and one of the world's highest paid actors, is busy filming in a dank room filled with dangling wires and ropes.

Johansson plays a character that appeared earlier in a manga comic series and animated film.

Portraits of the actress in character as The Major, a human-cyborg crime fighter, stare down from the walls.

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Her black-bobbed wig and make-up appear to nod to the film's Japanese roots. The story is based on the manga comic series created by Masamune Shirow. Which brings us to the elephant in the room. The assembled journalists have been asked – well, warned – to ignore the aspect of the film that has everybody talking: while Scarlett Johansson is more than capable of portraying a cyborg action heroine, she is decidedly not Japanese.

In the original comics and movies, the character's name is Motoko Kusanagi. She works for the law-enforcement division of the Japanese National Public Safety Commission.

There have been reports (denied by the production company Paramount) that the producers considered using digital tools to make Johansson look more Asian.

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Hollywood has a long-standing habit of casting white actors as Asian characters. Mickey Rooney's Mr Yunioshi in the 1961 film Breakfast at Tiffany's is a notorious example.

But it's still happening. In 2016's Doctor Strange, Tilda Swinton played the Ancient One, a monkish character who was depicted as a Tibetan man in the Marvel comic books. Emma Stone played a Chinese-Hawaiian woman in 2015's Aloha.

Representation and race are hot topics in Hollywood. The lack of diversity among the actors nominated for awards at the Oscars spawned a hashtag, #Oscarssowhite. Stars including David Oyelowo, George Clooney and Lupita Nyong'o have spoken out about ingrained prejudice in Hollywood, as has Barack Obama.

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So it does not seem unreasonable to ask Johansson for her thoughts. But Paramount's publicist, after a somewhat tense stand-off, tells the group that such questions should only be addressed to the filmmakers. "It's not for Scarlett to answer that question," she says. "We don't want to offend her and create any animosity or anything."

It's hard to know how much of this comes from Johansson herself. She is not shy about giving her opinion on other subjects. She is a supporter of the Democratic Party and is one of the many celebrities taking aim at President Donald Trump and his family. She recently played Trump's daughter Ivanka on television's Saturday Night Live. Her skit was a spoof ad for the fictitious perfume, Complicit ("the fragrance for the woman who could stop all of this, but won't").

She has campaigned for Obama and worked to engage younger American voters. The day after Trump's inauguration, she spoke passionately at the Women's March on Washington about female-focused health care and reproductive issues. "I'm not the type to divulge facts about my personal life," she said. "I am fiercely protective of my family and I have no social media presence. But I feel that in the face of this current political climate, it is vital that we all make it our mission to get really, really personal." She spoke about taking a trip to the gynaecologist at 15, citing her clinician's compassion and professionalism as evidence of the importance of Planned Parenthood, an organisation facing funding cuts under the Trump administration.

"President Trump, I did not vote for you," she said. "That said … I want to be able to support you. But first I ask that you support me, support my sister, support my mother."

There's no denying that a celebrity of Johansson's stature has the power to influence public debate – just as Hollywood blockbusters can have an impact on the way people think about political and social issues.

Ghost in the Shell might have been a career-making opportunity for a Japanese actress. "There are very few opportunities for Asian women to be kick-ass action heroes," says Tony Ayres, the Macau-born Australian director of films including The Home Song Stories and Cut Snake. "What we're missing from the studio system is courage ... Jennifer Lawrence was not a star before The Hunger Games, so why wouldn't you take a risk on an unknown Asian actor?"

In defence of the casting, Ghost in the Shell producer Ari Arad has pointed to the diversity of the other actors: French actor Juliette Binoche, Danish actor Pilou Asbaek, Fijian-Australian actor Lasarus Ratuere and Japanese actor Takeshi Beat Kitano. But that wasn't enough to satisfy the tens of thousands who signed a petition in 2015 calling for Johansson to be replaced.

Fans have recently taken out their frustrations by using a campaign website for the film to upload images of Asian actresses with captions such as "I am the woman that should have been cast".

Ghost in the Shell fans are passionate because they have been invested in this story for a long time. The original manga was published in 1989. Since then the cyberpunk crime saga has expanded into Japanese spin-off films, television series, books and video games, with stories that explore mind-bending questions about identity, consciousness and technology.

Interestingly, Johansson's casting seems to be less controversial among Japanese fans, many of whom responded positively to the trailer and apparently expected that a Western actress would be cast in the Hollywood remake. What's more, as some have pointed out, The Major's body is a machine, which arguably makes her ethnicity irrelevant.

When Johansson finally appears to answer questions in Wellington, she emphasises the ideas about consciousness and individuality bound up in the character.

"She is sort of reborn into this cyborg body," she says. "She has a very kind of murky idea of who she once was."

In that respect, the role is a good fit for Johansson, who has appeared in a series of sci-fi films that examine the relationship between women, their bodies and their minds. In the critically acclaimed Her (2013), she played the disembodied consciousness of a computer operating system, who forms a romantic relationship with a human man. In Under the Skin (2013), another critical success, she was a seductive alien being who preyed upon men. As the title character in Lucy (2014) she played a woman who gains psychokinetic abilities after absorbing a drug into her bloodstream. She's also played a superhero in a somewhat less cerebral sci-fi franchise – the Black Widow in Marvel's Avengers franchise.

Johansson says she is not a particular fan of science fiction but believes the burgeoning number of these types of movies is a reflection of the times. "[Ghost in the Shell] questions identity," she says. "How our relationship will be with advances in this digital age, how it affects our own identity, I guess, as a race of people."

The slew of science fiction is a relatively recent development for Johansson, whose long and varied acting career began when she was a child. She started auditioning for commercials but took rejection so hard that her mother restricted her to trying out for films.

From child and teen parts in films such as Manny & Lo (1996) and The Horse Whisperer (1998) she managed a smooth transition to adult roles – something that has proved a struggle for many other actors. While her looks helped (it's hard to find a list of the world's sexiest women on which she doesn't feature) it would be a mistake to dismiss Johansson as a mere femme fatale. Her breakthrough adult role in Sofia Coppola's Lost in Translation earned her the respect of critics. "At 18, the actress gets away with playing a 25-year-old woman by using her husky voice to test the level of acidity in the air," said the New York Times.

There's also been the odd critical mauling for films such as The Nanny Diaries.

Now 32, she is one of the most bankable stars in Hollywood and was reportedly paid $US17.5 million to play The Major in Ghost in the Shell. The film comes with all the high-tech bells and whistles of a big-budget action blockbuster. Among her costumes is a thermoptic suit made of silicon, which allows her to turn invisible – even on a chilly night in New Zealand it must be uncomfortable. "I don't wear it that often," she says. "It's not so bad ... It's kind of like wearing a wetsuit."

She says she has taken on "a lot of the responsibility" of performing stunts in the film. "I think there's an element of fear when you do anything that's really challenging physically, but that's part of what makes the action interesting to watch and drives you to really nail it."

For a long time, she kept quiet about the controversy surrounding Ghost in the Shell, but she did address it in an interview with Marie Claire in February. "I certainly would never presume to play another race of a person," she said. "Diversity is important in Hollywood, and I would never want to feel like I was playing a character that was offensive.

"Also, having a franchise with a female protagonist driving it is such a rare opportunity. Certainly, I feel the enormous pressure of that – the weight of such a big property on my shoulders."

In Wellington, she is sticking to more benign topics; what she thinks of the city (apparently not much – "it's a quiet place, people are nice") and how she has been spending her time here. "I'm pretty low key. I have a kid. We go to the zoo, do kid stuff." Johansson recently filed for divorce from her husband, Romain Dauriac, and the pair are negotiating for custody of their of two-year-old daughter, Rose.

When Johansson gets up to leave, she has graced us with precisely 11 minutes of her time. She offers thanks and one last thought: "One latex suit at a time." That's life as a superstar.

- The writer was a guest of Paramount Pictures and Tourism New Zealand.