In some forms of ancient Japanese theater, a skinny red stripe on the stage is all that separates heaven from hell. For decades, Japan's fashion designers have treated the thin glass of their storefront windows as an equally inviolate divider, cleaving the cool, exclusionary aesthetic of their boutiques from the rowdy street fashion of the teens preening outside. But enter Naoki Takizawa's sleek, stark space in Tokyo's fashionable Roppongi Hills neighborhood and the soaring glass wall seems less a barrier than an instrument for osmosis. Among his latest designs for haute-couture label Issey Miyake—fanciful blouses and blazers inspired by the flourishes of baroque furniture—mingle a more prosaic product: Takizawa's imaginative take on Lee jeans and Champion sweatshirts. "For too long, fashion was something people could look at but couldn't imagine wearing," says Takizawa, whose collaboration with the decidedly unglamorous American clothing companies debuted this spring. "I wanted to mix the street and art and create something totally new."

The goateed, denim-clad Takizawa isn't the only highbrow designer teaming up with street-fashion labels in a high-low endeavor that has rocked Japan's fashion scene. Last year, the icon of Japanese haute expression, Yohji Yamamoto, joined forces with Adidas to sell a new line of sportswear, tagged Y-3. This month, Puma will showcase its latest sneaker collaboration with Yasuhiro Mihara, Japan's version of a younger, spikier Manolo Blahnik. Ironically, the decision of these high-fashion designers to come down from their ateliers and mix with the skateboard set is less their own than the imperative of the one sector of Japan's lackluster economy that's still spending: the nation's youngsters. "Like it or not, we are defined by our youth culture," says Mihara, himself sporting a Grateful Dead T shirt and a baseball cap emblazoned with the word kooky.

At first glance, few would have expected this democratization of fashion to blossom in a nation famed for buying sprees that hurtled every citizen toward stylistic conformity. After all, who can forget the Japanese tourists who thronged exclusive boutiques in Paris or Milan, all loading up on exactly the same must-have purse or belt? Or the platinum-haired, deeply tanned kogyaru look that painted Tokyo teens like a badly conceived Hawaiian Tropic advertisement? But Japan today boasts a diversity of expression unmatched anywhere in Asia. Years of recession have galvanized a generation of faceless students, salarymen and office ladies to shed the uniforms they associate with the failure of the bubble years and probe unexplored fashion territory. "We've reached a point in Japanese society where people don't necessarily look up high for their fashion inspiration," says Takizawa. "In fact, even many older people have started to look to the street for inspiration, and that's making the whole culture more casual—and more creative."

Takizawa embodies that casual creativity. Born in 1960, Issey Miyake's heir apparent has overseen rarefied collections with names like Pressed, Shade and Smoothed Edges. But even as he was earning accolades from the jet set, Takizawa says he was drawing his truest inspiration from a little swatch of antique denim fashioned during California's Gold Rush. "For people of my generation in Japan, denim represented freedom and individuality," says Takizawa. With more younger buyers crowding his store, Takizawa decided it was time to debut this most plebeian of fabrics on the runway. The loosely tailored jeans that resulted from his collaboration with Lee are meant to go equally well with an Issey Miyake blouse or a no-brand T shirt.

Such a mix-and-match attitude, Takizawa believes, is particularly suited to Japan. In places like Paris, high fashion is a luxury earned through maturity. But in Tokyo, it's a birthright. Gaggles of young women live at home, piling up enormous disposable incomes that make them the one bright spot in an otherwise moribund economy. With even high-school girls able to afford a Louis Vuitton handbag, the cachet of haute couture is rapidly wearing off. "People in Japan no longer feel they have to prove they're rich by wearing expensive labels," says Takizawa, who himself rarely wears head-to-toe designer togs. "The whole ideology of fashion is becoming more inclusive."

Ultimately, though, the high-low collaborative trend may be little more than a fad. Because Japan's fashion industry depends on such a juvenile clientele, designers have had to adjust to even briefer fashion cycles. One top design house in Tokyo estimates that in order to satisfy the ever fickle tastes of young Japanese patrons, domestic labels have had to double their output compared with European clothiers'. The endless search for the next new thing, dubbed shinhatsubai in Japanese, affects everything from orange juice at the convenience store, which contains less pulp in the summer months, to ever so slightly different shades of khaki cargo pants for each season. Some fashionistas sniff that mix-and-match collaboration is simply this year's shinhatsubai. But the trend's champions argue that this craze might have a longer shelf life because it allows both the haute designers and street labels to diversify into each other's audiences.

For many Japanese designers, collaboration also allows them to piggyback on the success of already established street brands. Japanese are even more attuned than Americans to the iconography of consumerism. This is, after all, an animation-crazed culture in which characters like Doraemon, Hello Kitty and Pikachu adorn everything from refrigerators to boxes of seaweed sprinkles. Consumers, especially the key youth segment, prefer splashing out on recognizable icons—an almost Pavlovian response to a society awash in symbolism. No surprise then, that one of the details that Takizawa is most proud of in his collaboration with Champion is the way he reinterpreted the sweatshirt maker's embroidered "C" monogram into a tricolor abstraction. Shoemaker Mihara, too, stamped his sneakers with a cartoon rendition of Puma's feline logo on the soles—an animé-inspired touch that has won plaudits in Japanese fashion magazines.

Nevertheless, Mihara may eschew the cartoon soles for his next Puma collection. Even though the concept is popular, the 31-year-old designer knows it may not last beyond one season. Japanese fashion's ephemeral nature will force him to come up with something new—yet again. Luckily, Mihara says his consumers seem ever willing to experiment, an easy assimilation that mirrors his homeland's historic ability to import technology and imbue it with a uniquely Japanese aesthetic. "Every day, we reinvent ourselves," says Mihara. "It's exciting to think about what we may become tomorrow."

With reporting by Michiko Toyama/Tokyo