It's one of the best anime movies I've seen. From some points of view I'd even give it the number one spot, although I haven't yet seen Hosoda's highly acclaimed Wolf Children. I have that on DVD, though, and I must watch that soon. (However I have seen his The Girl Who Leapt Through Time and Summer Wars, both of which I liked a lot. This film is better. I'm also now absolutely determined to see his just-released Mirai no Mirai, which I believe shares this film's theme of parenthood.)
Admittedly it's less adorable than Ghibli, but it has a far stronger script than most of them. It's got a two-hour runtime and it earns it. I was startled to see halfway through that there was still another hour to go, because the story we'd had so far would have been enough for most anime films. A nine-year-old boy, Ren, is sleeping on the streets when he's picked up by a rough, rude monster called Kumatetsu. The Lord of the Beast World is retiring and Kumatetsu is one of the two candidates to replace him, but this seems crazy because he's got the brains of a hand grenade and the social skills of a poison gas massacre. He's been told by the current Lord to find a disciple, which is a challenge because no sane person would accept that position.
Kumatetsu horrifies everyone by offering to take in this young human. It soon transpires that Ren is as abrasive as Kumatetsu, partly due to his family circumstances. They get on as well as gunpowder and a burning match, which made Natsuki laugh quite a lot. (There's some good comedy here, although I should note that I'm a bad parent because the film's a 12-certificate in the UK. Natsuki loved all the Ren-Kumatetsu comedy, but his attention drifted in the film's more sophisticated, grown-up second half.) Kumatetsu is Not A Good Teacher, but Ren sets out to learn from him anyway.
They're both pretty terrible people... no, not terrible. Flawed. They have big personality defects, which means that they're stronger with each other (even if you'd have to half-kill them to make them admit it).
Then, in the second half, things stop being simple fun and get crunchier and interesting. The film's about fathers and sons. (Mothers aren't completely ignored, c.f. the powerful absence of Ren's late mother and the sometimes mother-like Kaede in the second half, but that would be an insultingly reductive reading of Kaede's role and in any case the film's examining some very masculine attitudes.) Interesting resonances come to light and, because this is fantasy, a few metaphors get made literal. The Moby Dick one is such a bold example of the latter that it'll probably seem like a bit of a head-scratcher if you're watching the film on a thuddingly literal level. What the hell? Why? It looks extraordinary and it scared Natsuki a bit, but... what? However one throwaway detail I love (and didn't notice at the time) is that the magic whale flying through Tokyo goes past a Starbucks... which was named after a character in Moby Dick! (I don't know if Hosoda knew that, though, and it might just be synchronicity.)
There's a lot to like in the script. I enjoy the effortlessness with which Iouzen's two sons switch between who's The Good One and The Bad One, which is both satisfyingly true to their characterisation and a reflection of future developments. I like the way Hosoda avoids glib Hollywood unity in Ren and Kumatetsu's stories. (The two characters need different things, despite their similarities, and Ren's journey is a whole lot more complicated than just being the agent of Kumametsu's own growth. There's still a real world out there and there are things that happen when a son grows up. Kumatetsu's going to be bad at handling that too.)
There's far more to this film than Ren and Kumatetsu, although of course they're always great together and it's a joy to see the final arena battle.
I'm sure this film wouldn't have resonated with me as strongly before I became a father, but I'd still call it a thoughtful, unexpected exploration of its themes that's using its genre to push in directions that wouldn't be available in a realistic story. Also, just as importantly, it's entertaining, cool and has great fight scenes. (Kumatetsu has that duel to prepare for and he's bad at thinking about anything else.) Both Natsuki and I also found it funny. However I should note that there are quite a lot of reviews on the internet that call the film overlong, generic and a bundle of tropes with nothing new to say about them. Personally I'd say these people weren't, uh, thinking very deeply, but it's still clear that a significant chunk of the audience didn't respond to this film anywhere near as strongly as I did.
I loved this film. I can't promise that you will, but I can't help that. I admire the development of both Ren and Kumatetsu. They're not role models, to put it mildly, but that's part of what makes them cool. (The abrasiveness of their relationship makes their entwined-but-separate journeys seem more interesting and honest.) Suddenly I've become a Mamoru Hosoda fan.