Butlers deliver service and comfort to their masters and mistresses. Yet this live-action film of Yana Toboso's manga boots viewers out of their comfort zone, twice over. First, of course, the film takes the batty idea of an elegant demon butler out of stylised drawings and into live-action. It's a tough call, as what can look perfectly reasonable in manga or anime can seem unwatchably campy when performed by real actors. Second, as the synopsis indicates, the film makes humungous changes to the manga scenario. Instead of the magic butler and a boy in Victorian England, now it's a butler and a teenage girl (sometimes disguised as a boy) in a future world so vague that it's barely a world at all.

Gone, then, is the strip's quasi-real context. Butlers, even demon butlers, made sense in Victorian England, but in a nonsense future they're more nonsense. Gone, also, are those naughty shotacon undertones of a dandyish butler tending to a preteen boy. Without these twin foundations, you're often left wondering why this Black Butler was made at all. Of course, it would be hard to recreate England with a Japanese studio and actors, and don't even ask about the shotacon. But that doesn't mean there was any point in making a Black Butler which changed things so greatly.

The leads are introduced in the middle of an investigation, with intrepid heiress Shiori (Ayame Gōriki) letting herself be trussed up by people-trafficking heavies until the elegant butler Sebastian (Hiro Mizushima) shows up from the shadows. The ensuing fight is elegant and acrobatic, with Mizushima good at twirling and whirling. Yet it rings hollow; there's just no sense that he's physically dispatching the goons coming at him. His rapport with Shiori is quickly established – Sebastian toys and trolls with her, drinking her exasperation – but his performance feels too preening, too self-conscious, to be truly cool. Then the plot and more characters kick in, and things go wrong for a long while.

At worst, Black Butler recalls an infamous franchise screwup, the 1991 film Highlander II: The Quickening, which also mucked up its source's premises and threw its audience into a stupendously dull future. Black Butler is never that bad, but much of the first half is pretty terrible. The future world, full of anonymous buildings and interiors, is ludicrous and insipid. Despite Shiori's lavish Versailles-style mansion bunged in the middle, complete with Technicolor flower garden, the film feels starved of substance – even the substance of a pulp pastiche, which was provided by the Victoriana in the manga and anime.

By the time the film's big mystery case is laid out, and the game's supposedly afoot – with international ambassadors turning up as instant-mummified corpses – you can still feel lost to the plot because it's so silly. Even the detecting makes little sense, though you barely notice that amid all the other off-key distractions: the cute stumbling maid (Mizuki Yamato) who's instantly irritating in the flesh; the unfunny, boring policemen filling screen time; weird plot devices, like world politicians who all go to exorcisms; and a drug-fuelled underground orgy scene which looks like a shoestring spoof of James Bond. The party comes to a nasty end that's unsavoury yet unmoving to watch. After all, the decadent victims feel less real than most anime fall-guys.

And yet, just when you've given up hope for the film, it turns a corner. It happens around the time there's a kick-ass twist in a gun battle, involving a seemingly useless character. It's very silly, we've seen it before, and yet the film finally starts being fun. The uptick continues with slicker twists and double-crosses; character confrontations with weight behind them; a superior battle for Sebastian; and a strong, stylish coda for both protagonists. To add to the satisfaction, there's an interesting, thematically potent backstory for the villain, though it could have been threaded better through the film.

All of that can't make Black Butler a good film, but it ends up an enjoyably bad one. Even Mizushima's preening gives way to an ambiguous but powerful charm, and Goriki's petulant irritation becomes a fatalist strength at the denouement. Fans of the anime and manga may finally buy into the film as a legit extension of the franchise. Newcomers who've never heard of Black Butler before will just be baffled from beginning to end.