The Kobe-based Yamaguchi-gumi are widely considered to be Japan's most powerful yakuza organisation.
Yamaguchi-gumi members are identified by a rhombus-shaped pin (looks like two triangles back-to-back pointing left and right), worn on the lapel, and also by their confirming tattoos. The yakuza-studying academic, Adam Johnson, has suggested that any member showing his pin and tattoos is capable of getting just about anything possible, anywhere in Japan. The group are thought to have close links with the dominant Liberal Democratic Party's powerbrokers.
The gang's most successful lines of business are thought to be the manufacture and trafficking of amphetamines, money-lending, and "hard" pornography. In 1992, the group formed a non-profit commercial enterprise in Japan known as the National League to Purify the Land, a charity ostensibly dedicated to the ending of illegal drug abuse.
A split in the leadership of the organisation in 1983 following several years of political infighting, resulted in a new group, the Ichiwa-kai being formed of some 13,000 former Yamaguchi-gumi, and led by its first oyabun (or "godfather" in the classical Mafia parlance) Hiroshi Yamamoto.
The Yamaguchi-gumi's "Designated Boryokudan" address is 4-3-1 Shinoharahon-machi Nada-ku Kobe-shi, Hyogo.
REFERENCES: ADAM JOHNSON, JAMES GRAHAM, THE AUSTRALIAN NATIONAL CRIME AUTHORITY, THE UNITED STATES SENATE STANDING COMMITTEE ON ORGANISED CRIME, MISCELLANEOUS INTERNET SOURCES