Naoki Numahata and his daughter Ei, 4, at their apartment in Tokyo. Photo by Shiho Fukada for The Washington Post

Children and clutter don't have to go together, says Naoki Numahata, a 42-year-old Japanese father so committed to minimalism that he'd make a monk look extravagant.

When his four-year-old daughter Ei wants to play, she doesn't go to a playroom or even a play corner. Instead, she gets a small basket that contains all her most precious possessions – a doll, a Minions tin with some cars, a yo-yo and a spinning top – and plays happily on the stark white floor.

Their 420-square-foot Tokyo apartment is small even by Japanese standards, and is almost empty. There is nothing on the kitchen counter. In the drawers: three sets of chopsticks, two sets of children's cutlery. The breakfast drawer contains a loaf of bread and a jar of honey.

There is no couch, only a table, a chair and a bench for two. The small bedroom contains a bed that Numahata and his wife share with Ei. His one concession to decadence: a big television that he uses for his work as a web designer.

He has only two pairs of pants, four shirts and four T-shirts, five pairs of underwear and four pairs of socks in the closet. Ei has two special occasion outfits on hangers and two small drawers for her regular clothes. Numahata says his wife is not a minimalist: She has five drawers for all her clothes, winter and summer.

This kind of extreme minimalism is not standard practice in Japan, but the concept of making do with less has become much more mainstream in recent years, an antidote to materialism and excess. For the Numahata family and others like them, less really is more.

The most famous proponent of this concept abroad is the Japanese declutterer Marie Kondo, whose "KonMari" method – she tells people to get rid of everything that doesn't "spark joy" – has swept through the West in recent years.

But minimalism and decluttering became a craze in Japan several years before Kondo arrived on the scene. Indeed, people here know the concept not as the "KonMari" method but as "danshari" – taken from three Japanese characters meaning "refuse," "dispose" and "separate."

"Modern society is all about getting more, more, more without taking account of your whole situation," said Hideko Yamashita, who was promoting the idea of danshari several years before Kondo arrived on the decluttering scene. (She considers Kondo something of an interloper.)

"With danshari, you need to determine what's contaminating you and get rid of it," Yamashita said in her sparsely furnished apartment in Tokyo, urging both a physical decontamination process of space and a clearing of the mind.

Toys belong to Ei Numahata, 4, sit on the floor at apartment of Naoki Numahata, who practices minimalism. Photo by Shiho Fukada for The Washington Post

Her book on danshari became an instant bestseller in Japan, and the concept has now become a verb in its own right. Japanese people don't talk about KonMari, they say: "Ah, my house is a mess. I need to danshari."

This is the opposite of the other recent exotic home trend: the Danish concept of "hygge" – creating a cosy space with rugs and candles and other things that make you feel warm.

Danshari is based on the idea that if you have a clutter-free environment, your mind will also be clear. Formulating it, Yamashita, who is 63, was heavily influenced by eastern religions.

Zen Buddhism and Shintoism taught her to think about what she needs right now and to get rid of impurities, she said. And then there's Tao, the philosophy that considers the natural order of the universe.

Many Japanese people of Yamashita's generation, born after World War II, became hoarders, unwilling to throw anything away in case they needed it in a time of emergency. There is a constant refrain here of "mottainai," or "don't be wasteful" – as in, better keep those 300 shopping bags in case you need them.

This clutter explains why so many Japanese people are unhappy today, she said.

"We have many depressed people in Japan. Their heads are too full of information, they become overwhelmed with their thoughts," she said. The process of getting rid of tangible belongings helps clear out intangible things, too.

Some psychologists have started "prescribing" danshari to their patients to get them to reflect on themselves, and Yamashita says danshari can even be good for relationships: Once you've decluttered, you're more likely to invite people home.