The Yakuza are the Japanese organized crime syndicate.
They arose as protectors of the common people during feudal times and have since spread outside of Japan wherever illicit opportunity exists in the modern world.
The Yakuza is made up of many different, and often rival, clans. The head, or "Godfather," of a clan is known as the Oyabun whose second in command is the saiko-komon.
Takeo Yamashiro, brother of Maseo, was tasked by his Tokyo Oyabun to retrieve the katana of his former sister-in-law, Tatsu, allowing his master to summon and control the souls imprisoned within the blade.
Katana and The Outsiders infiltrated Noguri Enterprises too late and were forced to retreat upon encountering the crime boss' resurrected warriors that were slain by the cursed weapon. They faced the Yakuza again, though this time Katana successfully avenged her husbands death by adding Takeo's soul to her mystic steel. Boss Noguri, on the other hand, managed to escape without consequence.
During the infamous gang war, a man named Akahara ran the Yakuza in Gotham City. He attended a gang-leader summit that went wrong, and was shot dead next to his katana-wielding bodyguard. His replacement, Niko, protected the gang from a takeover attempt by Orpheus.
One of the first criminal acts under Black Mask's command, was the reactivation of the drug trade in the city with help from Mad Hatter's mind controlling hats. Batman found a fraction of the gang and stopped their crime spree.
The Los Angeles branch of the Tokyo Yakuza was autonomously run by the octogenarian Oyabun, Shoko Ishiguro. Clan Ishiguro was a profitable organization, controlling a large portion of the heroin trade while expanding into prostitution and pornography. It was all run from the legitimate company, Ishiguro Technologies.
The powerful criminal operation was dismantled entirely in just a matter of days, after Ishiguro's young saiko-komon, Ame Okumura, was inadvertently possessed by the demon, Etrigan, inciting a disastrous chain of events.