"IN THE old days," laments the retired mobster, with a broad smile, slicked hair and a heavily tattooed body, "the yakuza served a useful purpose in society to solve civil disputes and keep the streets clean." He draws on his cigarette, the stub of an amputated little finger visible in his beefy hand. "Now", he goes on, "it has lost its samurai spirit to moneymaking."

Or perhaps, the yakuza--Japan's organised-crime groups that date from the 17th century--are getting squeezed. For most of the post-war period they operated openly: tolerated by the public, used by politicians and protected by police. Crime will happen anyway, went the argument, so better to know whom to call when it crosses the line. In the 1950s ministers and industrialists relied on the mobsters and...