Renzo Rosso is a floppy-haired fiftysomething who would blend in perfectly on a porn set, but instead runs Diesel S.p.A., the casual clothing megabrand.

Standing in his fancy new Aoyama gallery he’s admiring “Black Wind crosses meadow,” an artwork by Hiroki Tsukuda consisting of “mixed media and stuffed deer.” The ex-stag is wearing a black bomber jacket and plastic face mask, giving it the look of a cervine Darth Vader. Cheeky, playful and slightly disrespectful: it’s very Diesel.

“Yeah, I was impressed when I saw this because I just bought a big horse for my house,” says Rosso in his fantastically thick Italian accent. “A horse with a lamp. But I think this is much better than that. I want to buy this.”

Rosso paid a flying visit to Tokyo during Japan Fashion Week, which ended last Wednesday, to promote the Diesel Denim Gallery, a two-story space in swank Minami-Aoyama that juxtaposes avant-garde art with a select, high-end range of Diesel clothes.

On the first floor, limited-edition attire surrounds “Once Night Falls,” an installation of insects, covered in gray paint and hanging from chains under strip lights. There’s an artistic rationale to this morbid chic — something about senses and light and transforming boundaries. But the point is that Diesel can dangle dead insects in its swish new store because it’s the brand that puts bare bottoms on billboards in the U.S. and China alike, and approves ads with tag lines such as “Save yourself: Drink urine” and “How to smoke 145 a day. Who needs two lungs anyway?”

It’s a brand that oozes commercial counterculture, and the new gallery-cum-store is designed to crank the dial. As Rosso puts it: “Instead of going to sign a deal with a famous artist — it can be Madonna, it can be anyone — we think that if we start from scratch and build a relationship with new, upcoming talent, we can gain status.”

Nanzuka Underground, perhaps the leader of Tokyo’s avant-garde galleries, was tapped to curate the upper floor, pulling in Tsukuda for his Diesel-friendly mashes of manga and sci-fi fantasies, with titles such as “The One,” “The Other One” and “Get Together with a Suspicious Mythographer.” The style is brash, the imagery warped — but as Rosso’s colossal coffee-table tome “50” says, “warped minds think alike.”

Diesel isn’t the first fashion brand to co-opt the art world. Paul Smith, Gucci and Louis Vuitton have all blazed the trail in Tokyo. But Rosso’s brand is fudging the boundary more boldly than most. At the Diesel Denim Gallery you can spend ¥30,000 on a Tsukuda digital print, or more than double that for a pair of limited-edition denims from the fall/winter collection.

Is fashion art?

“I think that everything that’s beautiful can fit together,” says Rosso. “It can be a movie, can be art, can be fashion, everything must fit together. It means style — lifestyle.”

The original Diesel Denim Gallery opened in New York in 2001. Tokyo gets the first sister store-slash-gallery because, says Rosso, “Tokyo for me is the most fashionable town in the world. What I like about the Japanese is that if there is one trend, they will go to the maximum. And every day you go out you can see new things.”

As a 52-year-old in charge of a feisty youth label, Rosso could be forgiven for handing the creative reins to younger minds. But as he tells it, he’s still the driver of innovation.

“When something is working I tell my people, ‘OK, we have to change,’ and they get crazy with me,” he says. “They want to kill me.”

Rosso’s career has spat in the face of common sense. He picked Molvena, a town in northern Italy with a population of just 2,500, as his base instead of the fashion capital Milan. And when Italian designers were building reputations for suits and high-end style, young Renzo became an ambassador of casual wear.

“Casual means blue sky, green gardens, vacation,” he says. “Casual is the state of freedom.” And he sees his peers coming around to his way of thinking. “Thirty years ago when we started, a lot of people were in uniform, just in suits. And you can see that department stores today are only casual,” Rosso points out. “You can see, for example, that all the luxury brands are coming in the direction of Diesel. Gucci, Prada, everybody comes to invade the area that we made.”

And so, with typical contrarian flair, Diesel is moving upmarket. The Diesel Denim Gallery collection uses more luxurious fabrics — organic cotton and hand-sewn details — than the brand’s standard range. With limited-edition jeans selling at up to ¥75,000 per pair — double the price of their standard five-pocket range, these are fancy pants for the better heeled customer. But while prices have headed upmarket, the ethos sure hasn’t: the man from Molvena attended his gallery’s opening in a beaten-up T-shirt, rubber flip-flops and that famously tousled mane.

“Hiroki Tsukuda: Doctrine” runs till Nov. 18 at Diesel Denim Gallery, 6-3-3 Minami-Aoyama, Minato-ku, Tokyo; gallery open 1 p.m.-8 p.m. (store, 11 a.m.-8 p.m.). Hirofu Iso/Komainu’s “Once Night Falls” shows till Nov. 20. For more information call (03) 6418 5323