@DiMaggio: indeed there's a big difference between a gang and a mafia, but we're not talking about a gang. For me the Yakuze isn't a gang, but a mafia. Why? Because mafia for me isn't necessarily a Sicilian thing but a way of life/acting.
@ITB: Cosa Nostra is something the journalists and 'show off' mobsters of America made up. No Sicilian mafia called themselves Cosa Nostra.
@DiMaggio: Mafia isn't invented. It's not that someone at some time tought: 'well, if I do this and that, it will result in this...and I call that Mafia'. And if you still think that's true, why isn't it possible that someone else also tought this (meaning Japanese people who 'invented' the same)?