Much of the Steins;Gate TV series consisted of its time-travelling hero desperately striving to square circles, bending the multiverse to save the friends he loves. The film sequel, Steins;Gate Fuka Ryōiki no Déjà vu (Loading Area of Déjà vu), has its own circle to square. The TV show ended so well; its resolution was ingenious, exciting, heart-rending and visceral (No, not the fingers!). Moreover, Steins;Gate has already had a coda, an OAV story set in America, included as part 25 in the DVD/blu-ray of the series. A further sequel doesn't just risk being redundant, but also spoiling the memory of a stellar show.

Steins;Gate: Loading Area of Déjà vu leaps both hurdles with aplomb. True, it's not as good as the series. Nor does it redefine it, in the breathtaking way that the show's second half upped its game. The film also uses a hoary plot device done umpteen times in anime. It's the Disappearing Protagonist, where a key character mysteriously vanishes from the world. It's also a Self-Erasing Protagonist, someone who wilfully scrubs him or herself from reality and memory, rather than trouble anyone else. (The prevalence of the Self-Erasing protagonist in anime and manga is surely connected to Japan's romanticising of suicide.)

It's not really a problem, though. Steins;Gate has always pilfered familiar ideas, often from other time-travel tales; indeed, it's part of what made the show fun. Using a similar approach to Doctor Who, Steins;Gate concentrates on presenting its ideas in a Steins;Gate way, through Steins;Gate characters. And the film's main character is…

Kurisu.

Yes, Loading Area of Déjà vu is the tsundere's story. Kurisu was sometimes the viewpoint character on TV too; she even had the show's loveliest moment, with rain, shadows and the unification of relativity and love (“Right now, I feel like complaining to Einstein…”). This time, though, Kurisu is the chief character from the start. The film opens with her delivering a mystical voice-over (recalling Okabe's monologue at the start of the show). The titles follow her plane from America to Japan.

The next scenes obscure the focus by doing what a TV spinoff is mandated to do; bring back all our friends. Like sitcom characters, the Steins;Gate cast has hardly changed. There are some amusing hints of development, but the stress is on the familiar. Mayuri and Ruka are still adorable; so, in his strange way, is otaku Daru, subject of the funniest jokes, which feel affectionate rather than spiteful. We also get look-ins from Faris, Moeka, Mr Braun and his daughter Nae. They're basically cameos, though there's a satisfying mini-thread about how Mayuri complements Kurisu, the two paramount girls in Okabe's life. We also get a reminder of how frightening Moeka was in the series, without resetting her character back to 'brainwashed killer.'

Initially, Okabe and Kurisu do seem to reset to how they were at the start of the series. At first, it appears that the OVA, about the characters' post-series relationship, has been quietly retconned. Things become clearer when Kurisu loses her inhibitions at a rooftop party; the girl may be the scientific heir to Einstein, but she can't hold her drink! It turns out that, despite what happened in the OVA, her heart and head are still in conflict. Kurisu may feel her connection to Okabe in another life, but her rigorous intellect can't accept it. One of the film's chief points is that Kurisu's ‘character’ – the ruthlessly rational scientist – is as much a performance as Okabe's flamboyant madman, both strength and curse. Later, one of the pair must literally wear the other's persona, recalling a gag in the Back to the Future films where Marty and Doc Brown swapped catchphrases.

The main plot starts when Okabe vanishes from existence, leaving Kurisu with flickering memories of him and a mysterious message left for her. (Fans can probably guess who sent it.) From this point, Kurisu embarks on an adventure that's effectively a paraphrase of the TV series, which was already an exercise in doubling back on itself. The film presumes you know Steins;Gate well, often reworking scenes with Kurisu in Okabe's place. And yes, Kurisu finally gets to travel in time herself.

The revisiting of old territory has its drawbacks. The film has to recapitulate ideas from the OVA, for example, because a lot of viewers may have missed that. There's also a scene, involving a heated argument between Kurisu and Okabe, which recaps so much of the series that the film starts to feel alarmingly like a clip show. Moreover, there's a potentially confusing Easter Egg moment, when Okabe flashes ‘back’ to a bloody scene involving the little girl Nae, which never happened in the series. It's from the source Steins;Gate game, which is a clever meta-detail, but it'll have non-gamers scratching their heads and awaiting a payoff that never comes.

The film is essentially Steins;Gate as character drama, getting inside the head of Ms. Makise (she comments to Okabe that his journey through timelines gives him unfair access to what she regards as her ‘private’ thoughts). It's not an action film; it concentrates on the puzzles and dilemmas, not the gasp moments of the series. The first half of the TV Steins;Gate – the funny, leisurely stuff – felt akin to The Big Bang Theory, or some of the work by SF writer Connie Willis (To Say Nothing of the Dog). The later episodes played more like the thriller Source Code. The film, though, brings the franchise close to the book The Time Traveller's Wife; a time travel romance told through both male and female eyes, shaping each other like hands in an Escher print.

More modest and less surprising than the series at its best, Loading Area of Déjà vu still feels like Steins;Gate. There are moments when the film's sampling of the series feels plain parasitic, but the story which emerges feels true to itself, and forces the cast to be true to their selves as well. The film also looks pretty much the same as the show. A CGI plane bears Kurisu to Japan in the titles, but Okabe's Akihabara has changed very little from its TV incarnation. There are still the same white skies and subdued colours and interiors, suggesting insulated, highly subjective viewpoints (a bit like Serial Experiments Lain).

Like the series, the film avoids any real fanservice even when Kurisu showers, while the one big underwear gag… well, it's a refreshing change from the anime norm (and gets the biggest belly laugh). There's little of the bravura storyboarding that made some sequences unforgettable on TV, but then the film's not telling that kind of story.