The man once known as Maenoyu Taro has lost some weight since retiring from professional sumo wrestling. Once an imposing 170 kilograms, he has slimmed down to 150, a mere 330 pounds. It's not fighting weight, but still enough to fill out a bulky suit – and plenty to command the respect of the students he is training to join him as Mongolian sumo royalty.

History suggests their chances are good.

Sumo is woven deeply into the cultural fabric of Japan, where it has been played for centuries and still, to many, commands near-religious status. But today, no one dominates sumo as the Mongolians do.

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Mongolian Asashoryu was once called the Tiger Woods of sumo – "The Japanese are no good," he told an interviewer – but even that descriptor has fallen flat next to fellow Mongolian Hakuho, who has used his towering 6-foot-4 frame to rampage through what remained of Japanese nationals in sumo's record books. Last year, Hakuho felled a 44-year-old record for total tournament championships, which had been held by the legendary Taiho, with 32 wins.

Hakuho has now taken 36 championship titles, cementing the Mongolian chokehold on sumo greatness. Today, the three wrestlers who hold the "yokozuna" champion title, sumo's highest rank, are all Mongolian. A Japanese wrestler has not held the title since 2000. Only one Japanese wrestler has won a professional tournament in the past decade.

Sumo has become Mongolia's game. The sport was once fuelled by impoverished Japanese strivers. But Japan is now a wealthy nation, and many youth have little incentive to enlist for the punishing training that sumo requires. It was into this void that Mongolians leapt. Herder children possessed the requisite hunger for riches and hardiness, after enduring poverty and brutally cold winters on the grasslands in traditional round gers, also known as yurts.

They "grew up in these harsh surroundings. I think that makes them tougher, and also able to adapt to new environments," said Maenoyu Taro, whose Mongolian name is Naranbat.

But wild success on sumo's greatest stage has done surprisingly little to kindle interest in sumo in the birth country of its greatest stars. Local television audiences for sumo have shrunk, even as Hakuho racked up wins. Only a single school in Mongolia provides professional sumo instruction: Kyokushu Beya, where Naranbat is now a coach. It only opened in September.

Japanese sumo stables today count 23 professional Mongolian wrestlers. But only 15 Mongolians currently wrestle in Japanese high schools, which often act as a sumo farm league, according to numbers compiled by Naranbat. In other words, the current crop of amateurs is smaller than the number of professionals, hardly an indication of massive interest.

It's as if the top players for the New York Yankees were British – titans in a sport their own countrymen scarcely care about, said Mark Buckton, an amateur sumo wrestler turned columnist in Japan who is among the best-versed foreigners in the sport.

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"There is almost no sumo in Mongolia," he said. What that likely means is that the Mongolian sumo reign, "is ending now." When the current champions retire, "there's maybe one other guy who has a chance in the future. There's just nobody below that."

Or as Naranbat puts it, "In Mongolia we are a wrestling country" – just not a sumo wrestling one. Parents send children to learn traditional Mongolian wrestling, or other forms, such as freestyle or judo.

Sumo, meanwhile, has struggled.

"There are not many amateur sumo wrestling tournaments in Mongolia," said Naranbat, who, like many Mongolians, goes by one name.

Part of the reason lies in the nature of sumo itself, which is as much a culture as a sport. "If you enter sumo, you are supposed to become sumo," said Katrina Watts, a former sumo commentator for Japanese broadcaster NHK who is president of the Australian Sumo Federation and still does stadium announcing at international competitions.

"You have to fit in, you have to learn the language and learn the culture and be part of it."

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For many sumo wrestlers, that means leaving behind the culture they were born into.

The first foreign-born sumo champion, Hawaiian Chad Rowan – better known by his sumo name Akebono – became a Japanese citizen, was briefly engaged to a Japanese television personality and made a conscious effort to distance himself from his Hawaiian roots, declining offers of food and goods from home when he first joined sumo. He once said he wanted others to see him "not as a foreigner but just as a wrestler gaining promotion."

Mongolian Asashoryu bucked the trend by cultivating a bad-boy image. His flouting of some sumo traditions won him condemnation in Japan, but adoration at home. Hakuho, however, is a sumo wrestler with a Japanese wife who many Mongolians see as no longer one of them.

Sumo itself has sought to limit foreign influence of foreign wrestlers, with a long-standing policy limiting sumo stables to just one non-Japanese wrestler.

In Mongolia, meanwhile, some of the ingredients for sumo success are vanishing. The herder population is rapidly declining. Once heavily nomadic, Mongolia's population is today nearly as urban as Germany.

Still, Naranbat has begun coaching sumo in hopes of keeping the flame alive at home. Twenty students are now enrolled, after four recently left to join high-school programs in Japan. The Mongolian Sumo Association pays all of their costs. "I hope more kids will come to the school and sumo will be developed in Mongolia," Naranbat said.

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His best current prospect is Mendsaikhan, a 100-kilogram buzz-cut 18-year-old who has been sumo wrestling since the age of eight. "Asashoryu influenced a lot of kids," he said. "I want to be an amateur champion, and then go pro in Japan."

On a recent afternoon, Naranbat watched carefully as Mendsaikhan sparred with an older wrestler. They slapped and grunted as they heaved at each other. "You were a bit slow on the tachi-ai," the explosive initial charge, Naranbat counsels after Mendsaikhan gets thrown out of the ring. Then, when the student wins a bout, he encourages him to keep pushing with his head. "It's a good technique. Use that more often," Naranbat said.

Parked outside the gym lay the kind of prizes his young charge might one day strive for: a Bentley, Hummer and Greyhound-sized RV that are the spoils of Naranbat's sumo career.

To replicate that success, Mendsaikhan is studying Japanese and trains more than four hours a day.

But even he is hedging his bets. Only half his training is in sumo. The remainder is in judo, a sport that, in Mongolia, mints real glory. In 2008, judoka Naidangiin Tuvshinbayar won Mongolia's first Olympic gold medal, instantly making him a national hero.

"Mongolia won judo in Beijing. People know about that and send their kids to judo," Mendsaikhan said.

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Judo and sumo do not occupy exclusive worlds: wrestlers trained in other disciplines can conquer sumo, too. In fact, some attribute Mongolian sumo success to the fact wrestlers such as Kyokushuzan, one of the first to become a Japanese sumo professional, began with Mongolian wrestling, and used that background to bring new techniques and concepts to sumo.

Many Mongolian children nonetheless dream of their own country's wrestling mats, rather than the sumo ring.

Even Naranbat acknowledges sumo might be better off with less Mongolian success. A few more wins by Japanese wrestlers might be good for the sport in Japan, where waning television ratings and thin tournament crowds have reflected a diminishing appeal.

"I'm worried that Mongolians are too dominant," Naranbat said. "I'm thinking if a Japanese wrestler starts really competing with these Mongolian champions, then its popularity will rise."