Japan's police chief has vowed to smash the murky links between sumo and yakuza organised crime after a widening scandal over illegal gambling led to the arrest of a former wrestler.
The biggest scandal to tarnish Japan's ancient national sport in years has led big-name sponsors to pull out millions and put in doubt whether national broadcaster NHK will show the summer tournament next month.
As investigators seek to untangle the links between the big boys of sumo and the bad boys of the Japanese mafia, police on Thursday arrested a former wrestler, Mitsutomo Furuichi, 38, on extortion charges.
Furuichi, who reportedly told police that he is a former gangster, allegedly demanded hush money from a sumo wrestler who had been involved in widespread gambling on baseball matches and other sports.
"He is suspected of blackmailing the victim... and received 3.5 million yen (39,000 dollars) in cash," a police spokesman told AFP.
Media reported the victim of the extortion attempt was wrestler Kotomitsuki -- ranked second only to the yokozuna, or grand champion.
"We have to clean yakuza crime links out of the sumo world," said National Police Agency chief Takaharu Ando after the latest news to tarnish the sport that has been at the heart of Japanese culture for 2,000 years.
Those links became apparent last month when sumo officials were disciplined after it emerged that they had given ring-side seats at a sumo tournament to top bosses of the Yamaguchi-gumi, Japan's largest crime group.
Because NHK broadcasts of tournaments are shown in Japan's prisons, the ring-side seats allowed crime bosses to send a silent message of support to their members doing time behind bars, commentators said.
The sumo association censured those who made the tickets available to the gangsters -- but the case highlighted connections between two of Japan's most macho and mystery-shrouded institutions.
Sumo, based on ancient Shinto rituals, puts its wrestlers through punishing workouts and an austere and strictly hierarchical lifestyle in the isolation of their 'sumo stables'.
Once populated by tough country boys, and increasingly by foreign-born wrestlers, it is a world of 3am roll calls and gruelling workouts where only the toughest fighters last to reach the top.
About 90 percent of stables have allowed beatings of trainees and punishments such as forcing salt or sand into their mouths, the sumo association has said.
Many Japanese were shocked by the 2007 case of a stable master who ordered the "hazing" of a 17-year-old wrestler who died after being beaten with a beer bottle and a baseball bat. The stable master was jailed.
While sumo is a tough and cloistered world of male athletes, the true bad boys of Japan have long been the yakuza, whose heavily tattooed gangsters have spawned numerous movies, manga comics and fanzines.
The yakuza, who trace their roots to samurai gone astray during the 17th-century Edo period, traditionally relied on gambling, prostitution, loan-sharking and protection rackets as their bread and butter.
In recent decades they have turned to money laundering, deposit fraud, cybercrime and extorting huge sums from blue-chip companies by threatening to show up at their shareholder meetings.
They have operated relatively openly, entertaining close ties with politicians, and police have tolerated their existence as long as they have stayed on their turf and kept down street crime.
Amazingly for outsiders, yakuza groups themselves are not illegal and openly operate from large corporate headquarters.
Japanese organised crime counts about 82,600 members, according to the National Police Agency -- nearly half of them with the Kobe-based Yamaguchi-gumi, dubbed the "Wal-Mart of crime syndicates".