Meet Geminoid F. In many ways, she’s perfect for the movie business. She’s beautiful, engaging, and can carry out a director’s every request on cue.

Time after time, she replicates the same performance without the slightest fluff or fumble, and can work for weeks on end without complaint. You don’t even have to pay her. Just remember to plug her in at night so she doesn’t die on set the next day, and she’ll be fine.

Geminoid F is an android – a robot designed to look and act like a human being (although the one thing she cannot do is walk) – and the first of her kind to co-star in a film. That feels like something of a milestone, considering cinema is full of memorable android characters. But from the seductive “machine-human” Maria in Fritz Lang’s 1927 monolith Metropolis to Star Wars’ C-3PO, Blade Runner’s replicants, and the enigmatic Ava from this year’s Ex Machina, almost all have been played by flesh-and-blood actors in costumes. (The others, including Sonny from the Will Smith blockbuster I, Robot, are digital creations, brought to life with motion capture technology.)

'There aren't the droids you're looking for': C-3PO and R2D2 in Star Wars Credit: HO

But when Stanley Kubrick was first planning A.I. Artificial Intelligence in the Seventies and Eighties, the famously exacting film-maker wanted the central role of David to be played by what he is: a humanoid robot. Kubrick shot some test footage, but the technology wasn’t there yet and, in the end, when Steven Spielberg made the film in 2001 (Kubrick passed him the project shortly before his death), David was played – perfectly – by the then-11-year-old human Haley Joel Osment.

But 14 years on, something approaching Kubrick’s original vision has come to pass. Geminoid F is nothing but a metal skeleton, pneumatic actuators (far more responsive than motors), silicone and urethane. As synthetic humans go, she’s the real deal.

At this year’s Tokyo International Film Festival, Geminoid F made an appearance on the red carpet for the world premiere of her first feature (in a wheelchair: she can’t walk independently). The film, a science-fiction drama called Sayonara, is written and directed by Koji Fukada and follows the relationship between two friends in the aftermath of a nuclear disaster.

One, Tania, is played by the 27-year-old human actress Bryerly Long, and is dying of radiation poisoning. The other, Tania’s “companion robot”, called Leona, is played by Geminoid F. Leona is in a wheelchair due to a faulty knee joint and has no understanding of what dying means. (The film is very good, but by no means a laugh riot.)

Though a small number of other humans drift through the film, for the most part the two women are alone together, either reminiscing and reading poetry in Tania’s house or going for walks in the surrounding grey-gold countryside. Fukada adapted it from a short play of the same name by Oriza Hirata, which also starred Geminoid F and Long, and has toured Europe, the United States and Canada since its premiere in Japan in 2010.

When you first see Geminoid F on screen, it takes a couple of seconds for the realisation to dawn that she’s not actually human, but it makes her more fascinating to watch, not less. There’s a delicious eeriness to the tiniest details of her movements – the way she blinks as she talks, for instance, or adjusts her eye line to look directly at people while they talk to her – precisely because of the growing awareness that someone has specifically programmed them to put you at ease.

That someone is Geminoid F’s creator, Prof Hiroshi Ishiguro, who controls her every move remotely on a laptop. He’s a severe-looking man in his early 50s, dressed entirely in black: leather waistcoat, cotton shirt and smart trousers, with a thick thatch of soot-coloured hair on his head.

Geminoid F is the latest in a line of androids Ishiguro has created at Osaka University’s Intelligent Robotics Laboratory. An earlier model, Geminoid HI-2, was made in his own image, to the uncanny extent that its hair came from his own scalp. (Ishiguro took the name “Geminoid” from geminus, the Latin for twin.) It’s the female version, though, that gets all the work.

After the first screening of Sayonara at Tokyo, Ishiguro is in high spirits. The film, he says, is proof that “androids can express as much humanity as human actors; this is an epoch-making event.” The ultimate aim of Ishiguro’s experiments is to isolate the elusive property of what’s known in Japan as sonzai-kan: the sense of being in the presence of another being. There needn’t be another human around for us to feel it – great cinema gives us intense feelings of sonzai-kan, so for Geminoid F, acting seemed like a worthwhile career.

Andy Serkis, in motion-capture gear for Rise of the Planet of the Apes, 2011 Credit: Rex

Elsewhere in the film business, digital visual effects artists are fighting the same battle on another front. When you watch Gollum in The Lord of the Rings films, the blue Na’vi in Avatar, or the motion-captured simians in the new Planet of the Apes films, it’s vital that you feel as if you’re watching a living thing, rather than just a collection of pixels.

When a computer-generated or android character reaches that deeply unnerving point of “almost, but not quite” – like the empty-eyed characters in some early motion-capture films, such as The Polar Express – they’re said to fall into the “uncanny valley”. Tumble in too deep and the result can be ruinous. The 2011 animation Mars Needs Moms – one of the worst-affected films to date – was one of the gravest box-office bombs in history.

The uncanny valley is itself a Japanese discovery. Its existence was first noted in a 1970 experiment by Masahiro Mori, a robotics professor at the Tokyo Institute of Technology, in which the “likeability” of various human-like faces was mapped onto a graph. As the faces became more lifelike, their likeability ratings increased. But suddenly, at around the 85 per cent lifelike mark, the likeability score plummeted – before soaring back up again, just as quickly, as it approached 100.

Prof Mori’s experiment found that pictures of robots and cuddly toys appeared on one side of the valley, and fit and healthy humans on the other. But the image that appeared in between them that suddenly caused the drop in likeability was the face of a human corpse – and that any other face that was lifelike to a similar degree, even if it had obviously never been alive in the first place, would provoke the same kind of instinctual revulsion.

The reason we seem hard-wired to reject characters that fall into the uncanny valley is that they literally bring us face to face with mortality. Looking at them is like looking death in the eye – and having death look right back at you.

Sayonara is part of Ishiguro’s ongoing mission to push his androids from one side of the valley to the other. One of the few types of unliving things to fall on the human side in Prof Mori’s original experiment were bunraku puppets: an incredibly delicate traditional Japanese art form in which multiple human performers, all dressed in black, work together to bring an inanimate character to life. So perhaps it’s no coincidence that Long, Geminoid F’s co-star, sees Sayonara as “a new form of puppet theatre”.

Working on the film, she stresses, was not like acting opposite a mere prop. Instead, Geminoid F’s movements “were imbued with a soul” in the same way puppets are by puppeteers.

“When you’re acting, you can either take a naturalistic or a stylised approach to performance, where in the stylised version it’s all about gestures and form,” she says. “And I think this is an interesting experiment in how much real emotion can be elicited from a performance that’s nothing but form. It asks questions about how we can actually be made to feel things when they’re conveyed through acting on a screen.”

Fukada says he found himself asking those questions in relation to his cast. “People have said they see elements of humanity in the android, but I found myself seeing elements of android-ness in the humans,” he says. “Because in a sense, all we are is very complex, highly developed androids. And I hope the film encourages you to think about these things.” The jury at Tokyo, which includes the directors Bryan Singer and Susanne Bier, will have a chance to ponder it at length: the android is eligible for this year’s best actress award.

Alicia Vikander in Ex Machina

Geminoid F’s facial expressions are controlled by just 12 pneumatic actuators underneath her silicone skin. That means she’s a relatively subdued performer – the Nicolas Cage android may be years off – but as Ishiguro notes, many of the best screen actors have been blessed with uncomplicated faces.

“Simplicity leaves room for our imaginations to be stimulated,” he says. “Conventionally beautiful faces don’t have many unusual characteristics.” His words echo Roland Barthes’s 1957 essay “The Face of Garbo”, in which he attempted to decode the face of the great Swedish-born Hollywood actress Greta Garbo – one of the simplest and most beautiful in the history of cinema.

“It is not a painted face, but one set in plaster,” Barthes wrote. “In spite of its extreme beauty, this face [is] not drawn but sculpted in something smooth and fragile… Garbo offered to one’s gaze a sort of Platonic Idea of the human creature, which explains why her face is almost sexually undefined, without however leaving one in doubt.”

There’s a lot to unpack here, not least of all the question of what on earth a Valentine’s Day card from Barthes must have read like. But what he recognised in Garbo is that a face as pure as hers can give us existential chills that go beyond mere human attraction – a kind of “uncanny peak” that lies beyond the edge of Prof Mori’s graph. Geminoid F is a way off it yet. But it’s a mountain she and her creator are ready to climb.