Big Man Japan is a mockumentary about Masaru Daisato (director/co-writer Hitoshi Matsumoto), who just happens to be a superhero who can grow to an enormous size and fight monsters that threaten the city. Daisoto is also a middle-aged, almost-divorced father who rarely sees his wife and daughter, takes care of his senile grandfather (who was also a superhero), and lives alone. He is considered a nuisance to the city for all the destruction he causes during his fights, and because of his ineptitude TV airings of his fights have been moved to 2:30 am (after paid programming) instead of prime-time, resulting in low ratings. Daisoto's agent also wants him to wear stickers of his sponsors during his fights, much to his disapproval.
The film is actually much better than I expected. Sure, the visual effects are cheap and incredibly unrealistic, and the fights themselves don't convey ineptitude so much as laziness (though one particular fight involving a baby does succeed in the former). But the monsters are imaginative, and the film itself is very inventive in its approach to the life of a man who was not meant to be extraordinary. Daisoto is presented in a cartoonish way, which helps the audience form an emotional connection to him, and the film is commendable for not treating him as the butt of a cosmic joke, but rather as a man who's, ironically, powerless in several different ways.
The film's fatal flaw, however, is its bizarre third-act, which comes out of left field and feels like a cheap shout-out to another corner of Japanese culture that is completely out-of-touch with the rest of the film. For the audience, its a cheat; for all the emotional investment and wit put into the first two-thirds of the film, Matsumoto throws it all away in favor of...well, I'm not entirely sure what's going on. Maybe I just don't "get" Japanese humor.
Overall, though, it's at least worth a look. With a different ending, this could have been a Japanese comedy worthy of Christopher Guest comparisons.