In the movie “The Devil Wears Prada,” which opens in Japan next month, an imperious fashion magazine editor played by Meryl Streep upbraids her new assistant, who has dared to snicker at a cerulean belt that the editor is considering for an ensemble. With withering condenscension, the editor somehow connects the belt’s history to the assistant’s frumpy knit sweater, explaining how every piece of apparel available today is a descendant of some haute couture decision made in the past. Basically, it’s an economics lecture.

The Japanese fashion designer Hiroko Koshino made a similar point in an interview that appeared in the NHK documentary special “Tokyo Kawaii Wars,” which aired Sept. 24. Koshino said that she believes her role in the fashion world is to be a “pioneer” — to create trends that in the long run will affect the way women dress. For that reason, she doesn’t think she should be expected to respond to what women want now.

This view of high fashion — that its social function is much more significant than nonbelievers give it credit for — was challenged by the program, which looked mainly at the ascension of what is called the “real clothes” fashion business, a grass-roots movement that has become so huge in Japan that the traditional fashion houses have been rendered anachronistic, regardless of how forward-looking they pretend to be.

The gist of this populist trend, which emerged from the teens-to-20s female demographic that patronizes the 109 building in Shibuya, is embodied in the title of the special. Kawaii, certainly the most overused word in the Japanese lexicon, means more than “cute.”

When uttered during the program, it denoted a connection between the consumer and the merchandise that is intuitive. Just as Koshino believes that her sense of style is derived not from her training, but from her personality (“it’s just my ideas”), the premise of real clothes is that their appeal is immediate. No one thinks about why something is good or bad. They just decide at the moment if it’s kawaii or not.

Consequently, fashion mavens are less important than peers. The single most important person in the real-clothes world is not a designer, but a model — Yuri Ebihara. A fixture in the girly fashion bible Can Cam (it has a monthly circulation of 800,000), “Ebi-chan” can make any piece of clothing a best-seller simply by putting it on.

In the program, she advises a pantyhose maker whose sales have decreased by half in recent years on how to gain a foothold with young women. When asked how she judges a particular dress or pair of shoes, Ebihara simply says that her only criterion is whether or not “I want to wear it.”

Many of the brands sold at 109 are not designed by “professionals,” but by girls who began working as sales assistants themselves, hardly any of whom it would appear have any training. One boutique hired two 20-year-old women to research and come up with ideas for a new line. They went out on the streets of Shibuya, observed what the kids were wearing, and then consulted with a dozen friends (the pair claims to have a “network” of 400 girls). They gave their ideas to the boutique owner who sent them to a pattern-maker in Korea. Less than a week later, the clothes arrived in Shibuya and went on sale. They were a hit. From concept to sale, the business cycle took only two weeks.

Compare this to the normal six-month cycle for high fashion. Fashion designers create clothing for journalists, other fashion designers and a small high-spending elite, so they aren’t committed to pleasing the average consumer.

That’s why fashion shows are so important. The experts pass judgment on this season’s collections and the more successful ideas eventually trickle down to the hoi polloi, in most cases years later.

Real clothes were not on display at last week’s Paris Collections, but they did make a whirlwind appearance at the Japan Expo in Paris 2006, which was mostly about anime and manga. Befitting the real-clothes mind-set of now now now, each brand was given a mere five minutes on the catwalk at the fashion show that was incorporated into the expo.

In order to demonstrate clearly how the stakes have changed, the documentary profiled one veteran designer who was once very successful, but whose brand has since fallen by the wayside. He hires a young merchandiser who quietly, but effectively, shuts the old guy out of his own business, hiring designers, setting up a Web site to sell the clothing on both computers and cell phones, and then launching the new brand three months after he was hired. They sell 8.6 million yen worth of clothing during their first 24 hours in business on the Net. The old designer has no idea what they’re doing, but he’s happy.

The real-clothes market has its own giant fashion show called the Tokyo Girls Collection. Whereas the audience for Tokyo Fashion Week is made up of professional elites, Tokyo Girls Collection is made up of girls: the very people who will buy the clothing on the runway.

Nobuyuki Ota, CEO of the Issey Miyake fashion house, who also heads Japan Fashion Week in Tokyo, attended the Tokyo Girls Collection last March and was knocked for a loop. “Everybody looked so happy,” he says, and the implication is stark. Haute couture is such a serious business, especially in Tokyo, where few young designers have emerged to challenge the 1980s pioneers who re-energized the international fashion scene back in the day. Those designers are now stuck in the rut of their own self-imposed reputations.

As Ota points out, this sort of grass-roots fashion revolution could have only taken place in Japan, and according to “Tokyo Kawaii Wars” the reason seems to be that Japanese women know what they like and aren’t easily influenced from above. The gap that traditionally separated the art of high fashion from the commerce of real clothing has been closed by young female Japanese consumers. It’s an economics lesson you can take to the bank, or the store.