Its parent TV series was surprisingly good, but this film's a little disappointing. It's basically another TV episode and not even a particularly good one. It's only got enough plot for 45 minutes, while the storyline isn't really testing the characters (either regular or movie-only). It's okay, though, and I'm glad I watched it.
It starts with a busjacking that would have broken the TV series's budget. That's cool, but after that the film spends a while drifting with our footloose monsters and not really going anywhere. It's quite nice, though. I like these versions of Bem, Bela and Belo. (Fuku Suzuki is visibly older, incidentally.)
After a while, the film potters in the vague direction of a plot. Belo befriends Michiru, a girl his age with a bad leg and a missing mother, Sayuri. Something happened. What unfolds from this is quite good in one sense, tempting our heroes once again with the possibility of becoming human... but it's not dynamic. Michiru and her parents aren't really being challenged as people. They're nice. They have warm scenes. I liked them, but their story is clearly less character-driven than most of the TV episodes.
The show's regular cast all return, which is pleasant but feels more like a sop to the fans than something the story needed.
The acting's mostly good, but I'm not sure about all of it. A couple of Sayuri moments didn't feel right to me. That said, though, the film's confident enough to put weight on the child actors. They live up to it. Suzuki's solid and arguably the most important of the three regulars, while Michiru's actress (Rina Hatakeyama) is lovable. I don't think she's still acting these days, incidentally, but Suzuki definitely is.
Is this a bad film? No. It's never worse than "okay" and it's capable of powerful emotional moments, e.g. our heroes' semi-tragic police siege goodbye. I liked Michiru's belief that monsters are kind and the ways in which the film underlines our monsters' immortality. The film dawdles a bit and I won't be watching it again, but there's nothing really wrong with it.