There are thought to be nearly 100,000 Yakuza members in Japan. When they enlist in individual gangs they are taken to a secret location where they are trained in hand-to-hand combat and meditation.

Last year, a yakuza boss in western Japan sued his former mentor over the gang office. The old boss had filed papers to transfer ownership of the office to a company headed by one of his relatives.

It expanded significantly from the late 1950s to the early '70s, becoming the most powerful yakuza gang in Japan. The year 2005 proved to be a pivotal one for the group, as two new leaders took ...