If this film were made with baseball or football as the subject matter, no one would consider it any different from any of the countless films since The Bad News Bears (1976) that relied on the formula: "smorgasbord of unathletic stereotypes brought together almost by force to compete in sport discover the meaning of teamwork and dedication and beat a good team in the end."
But the subject matter is sumo and the setting a Japan that doesn't respect its traditional sport very much, so it gets a lot more credit for that simple matter.
And yes, this film relies heavily on putting a bunch of stereotypes together. There's the unathletic coward who loves the sport, the fat guy, the inappropriately thin guy, and the girl who wants to compete in a man's sport. Perhaps the most interesting character is the European, in this case. A rugby player, he speaks fluent Japanese, loves to wield it to criticize Japanese society, and is compelled to join the sumo team so he has a place to stay. While he's not a very good actor, the character was very compelling.
Like in The Big Green (1995) or The Mighty Ducks (1992), the stereotypes are EVERYTHING here. The characters are otherwise extremely poorly developed. The fat girl wants to join the sumo team and it's suggested it's because she's in love with the skinny guy, but later on it seems she likes the sport for its own sake. The foreigner doesn't want to compete if he can't cover his thighs (someone who is so serious about Japan presumably knows what sumo is and how it's done, so shouldn't have any special problems with going in in traditional dress? It's not like he needs a hijab for spiritual reasons). The fat guy is Christian for no reason other than for the male protagonist to shout FREEDOM OF RELIGION during competition when a referee seems uncomfortable with seeing him praying. Or perhaps it was simply because all these movies always have to have one Christian guy who prays during the games?
The main place where more development could have really helped, however, is in the character of Misa Shimizu, an attractive young woman who's obsessed with sumo. At one point she goes on a date with the male protagonist, but no romance is implied. The skinny guy is pursuing her apropos of nothing and becomes depressed when she rejects him. At one point it's hinted she feels great admiration, attachment, or even love for the head of the athletic department she works with, but this isn't developed beyond a few lines.
And therein lies the heart of the movie. The only reason to watch it is to see a young Misa Shimizu prance around in a variety of autumn outfits, much like the only reason you'd watch The Big Green is for Olivia D'Abo. Nobody would be talking about this movie 2 months after it came out in theatres if not for that and the fact that it's about a strange sport (sumo). Although the latter shouldn't really have much of an effect either. Who's still talking about Dodgeball (2004)?
Honourable Mentions: The Bad News Bears (1976). Why does Bears work when so many of these movies fall flat? Could it be the iconic performance of Walter Matthau as a comically washed-out and apathetic ex-professional? I think it comes down to the character of The Bad News Bears. See, the Bad News Bears is composed of a bunch of unathletic unsportsmanly stereotypes, but each individual player doesn't matter. The team as a whole seems to have a personality of its own - one that mocks the sport they're playing, makes light of athletics as a whole, and has an irreverant disregard for anything serious. Its purpose and character is extremely well-defined, and you can't expect anything to happen other than what inevitably does.
