The Yamaguchi-Gumi, one of the world’s largest and most ferocious gangs, is estimated to earn over $6 billion a year from drugs, protection, loan-sharking, real-estate rackets and even, it is said, Japan’s stock exchange. This year, the organisation’s 100th, over 2,000 of its 23,400 members split away, leaving police nervous about what fallout might follow; a war between rival gangs in the mid-1980s claimed over two dozen lives. And yet membership of the yakuza—as Japan’s crime syndicates are known—is not technically illegal. Finding a mob hangout requires little more than a telephone book. Tokyo’s richest crime group has an office tucked off the back streets of the glitzy Ginza shopping district. A bronze nameplate on the door helpfully identifies the Sumiyoshi-kai, another large criminal organisation. Full gang members carry business cards and register with the police. Some have pension plans.