Hirokazu Kore-eda’s new film is a bafflingly unsatisfying and unconvincing muddle of ideas and moods; it is a futurist fable of AI-humanoid robot children, unpersuasively performed in a returning keynote of bland serenity. It is perhaps comparable to Kore-eda’s 2009 film Air Doll, a more adult story of man whose sex doll secretly comes to life.

Otone (Haruka Ayasi) – an architect who appears to work from home, with no office scenes or colleagues visible – is an educated woman married to down-to-earth Kensuke (Daigo Yamamoto), a carpenter who likes beer and playing baseball. Two years previously, their seven-year-old son, Kakeru (Rimu Kuwaki), was killed by a hit-and-run driver who has never been caught. They are approached by a company called REbirth, whose offices are huge and white with creepy logos and designs, like all sinister corporations in the movies, although the question of whether REbirth is supposed to be sinister is one of the film’s many unanswered questions.

REbirth offer a promotional free offer: an ultra-hi-tech humanoid robot replica (or replicant) of Kakeru, whose physical form, speech patterns and memories they can fabricate using videos, photos and other research materials provided by the stricken parents. The new Kakeru can stay with them for however long it takes to get through the grieving process. And when this stunningly convincing Kakeru 2.0 is delivered at the couple’s home, the audience will surely be expecting some emotional fireworks or, if those fireworks are absent, then a surely a very significantly numbed lack of emotion. But we get neither: Otone and Kensuke are bizarrely matter-of-fact; they behave as if some very sophisticated iPhone has been delivered. Otone’s mother faints when she sees the robot – but recovers quickly.

Otone wants to make a success of their new arrival, while Kensuke is grumpily unsure about the whole idea. He harshly tells “Kakeru” not to call him daddy – an instruction which has its ironic backlash when the police suspect him and “Kakeru” on the street of being a paedophile and victim. It’s a subplot punchline of sorts, not quite funny, not successfully serious. The tonal oddity of the film continues, trying to be a sci-fi dystopia and yet also a relatable heartbreaker about parental grief; these two modes simply undermine each other. Nor does the film attempt comedy, as in Spike Jonze’s Her – the intention is always seraphically serious.

Kensuke at one stage brings this “Kakeru” to the scene of the hit-and-run crime that killed their son, to see if the robot will remember or recover details of the culprit’s identity; this is a rather clever Hollywood-ish idea, one of many the film doesn’t pursue. He also uses “Kakeru” as a kind of confessor to whom he can admit his own guilt about the boy’s death; this idea is also left undeveloped.

Yet it is not enough for the film to ponder the existence of just this uncanny-valley robot child. It turns out that other abandoned or otherwise feral robot children have made contact with “Kakeru”, effectively planning a kind of replicant revolt, representing a yearning for freedom which the film finally appears to endorse. (As with other films about rebellious AI robots, you have to wonder about battery life.)

And so the film finally comes to its end, unsatisfying and baffling to the last, accompanied by its dreamy-sweet music. There’s nothing wrong with film-makers leaving their comfort zone and going for a big swing but this just doesn’t work; it isn’t as interesting as films on similar themes including Kogonada’s After Yang and Benjamin Cleary’s Swan Song. The story is misconceived and Kore-eda’s quietist, un-emphasised style doesn’t suit it.