In a society otherwise marked by gentle formality and good manners, the Japanese crime syndicates known as the yakuza have for decades been linked to murder, money laundering, racketeering and pornography.
In recent years, they have expanded to lucrative real estate and stock market scams, according to Japanese media reports and yakuza experts.
The yakuza, slang for the losing hand in a card game, have an estimated 85,000 organized crime members and associates.
Many Japanese consider yakuza members cult heroes who openly flout the rules in their restrained society.
Fan magazines and Internet sites track the love affairs and leadership changes of a colorful crime culture that in the past has featured elaborate tattoos, severed digits and fancy cars.
Some yakuza members carry their affiliation on business cards and maintain informal links to police and politicians.
There are even yakuza public relations drives: One syndicate bragged that it distributed millions in aid to survivors of the 1995 Kobe earthquake.
The gangsters hold regular business meetings, where police monitor them as they come and go with their bodyguards.
By far, the biggest syndicate is the Yamaguchi-gumi, a Kobe-based group that experts say includes nearly half the mobsters in Japan.
In recent years, the Yamaguchi-gumi has staked out turf in Tokyo, precipitating a series of gang wars that have killed 30 mobsters since 1997, according to a 2006 report by the Japanese National Police Academy available on the website of the National Police Agency.
In 2006, the yakuza accounted for more than half of Japan's methamphetamine arrests and 70% of arrests for gun possession, the report said. There were 21 gun-related murders and 97 armed robberies attributed to yakuza members.
Even for high-profile public figures, the threat of yakuza violence remains strong: Last year, Nagasaki Mayor Iccho Itoh was shot dead outside his campaign headquarters.
Tetsuya Shiroo, a yakuza boss, was sentenced this week to death in the case.