“JAPANESE PEOPLE DON’T CARE about resale value,” says the architect Sou Fujimoto, explaining why clients have allowed him to create houses that lack conventional versions of walls, ceilings or floors, and which require the skill of an acrobat to comfortably inhabit.

Fujimoto’s goal isn’t just to make spaces—the basic function of architecture—but to make people relate to spaces in new ways. Watching the couple move around the house, approaching everyday activities with the finesse the unusual design requires, suggests he is well on his way to achieving it.

Fujimoto photographed inside House NA in the Tokyo neighborhood of Koenji.
Fujimoto photographed inside House NA in the Tokyo neighborhood of Koenji. © Photography by Nobuyoshi Araki for WSJ. Magazine

He concedes that his clients have accepted “some really extreme solutions” to their housing needs. But rather than make their lives difficult, he says, he hopes to bring people “some comfort that is yet unknown.” That comfort may derive in part from landscape elements that Fujimoto blends into his buildings. During a tour of his studio in Tokyo’s Shinjuku neighborhood, the architect points to dozens of model houses with tiny trees breaking through walls, floors and ceilings. In Fujimoto’s hands, nature sometimes overpowers the built environment, a vision that could be apocalyptic were it not for his highly refined aesthetic. “I call it primitive future,” he says of the natural-artificial mash-up he is pioneering.

This fall, one Fujimoto building will help draw attention to Miami’s Design District during Art Basel, while another, in one of Tokyo’s main shopping districts, will compete with dazzling structures by the likes of Toyo Ito and Herzog & de Meuron. In California, Ronald C. Nelson, the executive director of the Long Beach Museum of Art, has been working with Fujimoto on ways to give the museum, in what was once a Craftsman-style house, new visibility. “We want a signature piece that says, ‘Oh, my God, I’ve got to go over there,’ ” says Nelson, explaining his choice of Fujimoto

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If his employees work in close quarters, that doesn’t bother Fujimoto, whose work is often about doing more with less—about, as he puts it, fitting architecture to the human body. Toshiko Mori, a New York architect and the former chair of the architecture program at the Harvard Graduate School of Design, says Fujimoto has a gift for devising structures that “create small moments of connection.”

That was nowhere more evident than in the pavilion he designed for London’s Serpentine Galleries in 2013. Each year, the gallery commissions an architect to create an event space in Hyde Park. (Fujimoto is the youngest architect to receive the prestigious commission, which has been awarded to Frank Gehry, Rem Koolhaas and Hadid.) His novel design wove thousands of steel bars into a kind of high-tech hedge. Transparent disks, set on the bars at various levels, became steps, tables and chairs. It allowed visitors to shape their own experiences, at different levels, the way children might choose different perches on a tree. At the same time, the pixelated structure blurred the boundary between indoors and out.

When Fujimoto has an idea, he may use it more than once. In fact, he is hoping to build a 1,000-foot tower in Taichung, Taiwan, that bears a strong resemblance to his Serpentine Pavilion. The Taichung government hopes the scaled-up version will become a symbol of that city—a kind of cloudlike Eiffel Tower.