It's Takashi Miike in Yatterman mode, i.e. a freakily faithful adaptation of an anime for six-year-olds. It's funny, but almost plot-free and a slog to get through.

The original anime started in 1993 and it's still going twenty years later, with an episode count that'll soon be pushing 2,000. Its Japanese name is Nintama Rantaro (Rantaro the Kiddie Ninja) and it's about a small boy called Rantaro and his friends at ninja primary school in the early 16th century. Each half-hour episode is itself split into two fifteen-minute sub-episodes and it must be very successful at what it does. I've never watched it, although I've seen glimpses.

As with Yatterman, Miike's film looks exactly like the anime. Unfortunately this time he's not getting to go nuts with giant robots, but it still means some outrageous facial prosthetics and unnaturally literal anime/manga translations like those "I've been clobbered" red bumps on people's heads. It's like someone nailed a golf ball to their skulls. Other assaults on realism include a small boy who keeps getting thrown out of a window to what must be a forty or fifty foot drop on to the mountainside below. ("It's okay," we're assured as we see him lying brained on a rock. "You don't have to worry about him. He's got a tough head.") There's a ninja hairdresser who inflicts haircuts that extend two feet from your head and look like ornamental sculpture. The un-villainous villain has testicles for a chin. Two characters have cheeks so swollen as to suggest elephantitis.

...and so on. You get the idea.

I'd have really liked this film, if only it had had a story. That absence puzzles me. Children are a tougher audience than adults and it's not generally thought that children's films don't need a storyline. As with Yatterman, I presume this is simply fidelity to the source material. Nothing is deep. Nothing really means anything. The villains aren't evil, but instead are cuddly and amusing. Testicle Chin is very funny, actually, and one of the best things in the film. I don't agree with the decision to keep everything trivial and inconsequential, but I presume it's in line with the original show.

Mind you, everyone uses real weapons and has superpowers. These are mega-ninja, of whom even one of the older classes could probably take down a small army. No one ever gets hurt in this film, obviously, but we still have six-year-olds hurling real shuriken and old men who can knock them out of the air and do backflips around them.

In fairness, a sort of plot develops in the second half. Rantaro and his friends have to win a race for the sake of the camp musical ex-ninja hairdressers. There's no danger or tension, obviously, but it gives the film a framework instead of being yet more random nonsense. However at the end of the day, this is essentially a bunch of gags and kiddie-pleasing set pieces with adults falling into pit traps and so on. (They dig a lot of pit traps. Couldn't they have varied it a bit?)

The acting's surprisingly good. There's some adult talent under that make-up (e.g. Terajima Susumu), but of course it's the children who matter. Rantaro's played by a child actor who's been working since he was 13 months old and has done a ton of TV, movies and voice-over work. He's in the 2010 Zatoichi. He's the Japanese dub's Max in Where the Wild Things Are and Mumble in Happy Feet. He won't blow you away or anything, but he's solid and he sets the tone. All the boys are so convincing, in fact, that it seems likely that it was the plan all along to bring together an army of them and let their collective energy carry along their performances. Small boys are small boys. Unleash a mob of them and you'll have an unstoppable monster, which is exactly what the film needed. They're great. Note that the only weak line readings are from the girl ninja, who only pop up briefly and aren't called on to interact with anyone.

The sets and costumes for those girls are a pink apocalypse, by the way. Imagine a world in which no other colour exists.

The frustrating thing is that almost everything in this film is as you'd want it. Many gags are excellent, both for children and adults. You don't need to be a child to appreciate jokes about farting and dog poo, but I think adults will better appreciate the melodramatic "save yourself" dialogue and its punchline. You'll be impressed by the surrealism value of a film that's eagerly adhering to a model so violently at odds with reality. Note for instance the scene in which Testicle Chin is converted to the side of good by the sight of a naked old man's penis. Then there's a guy who looks like Batman's Deadshot and will tear open the universe in order to deliver some exposition, before returning back to his dimension of primordial chaos and letting the movie continue.

However that's not all. The production values look quite expensive. The energy levels are admirable. The adult and child actors are all hitting the right tone, instead of (as might have happened) hamming it up and making the film unwatchable. There's a lot of fun in here and I can sort of understand the international distribution it's received, albeit largely on the back of Miike's name. However you'll have done well if you battle through to the end and I couldn't recommend this in more than fifteen-minute doses. It's charming, but it's also wearing.