I lived in China for some time and have a few friends that moved to China, got married there and are now working in export. Honestly I don't think the criminal organizations have any grip on Mainland China at all. Gambling is rampant, but is mostly conducted by local opportunists. Prostitution and drugs are barely noticeable. There's definitely corruption going on regarding construction and finance, but it doesn't seem to be traced back to any large scale criminal organizations. Counterfeiting is widespread as well, but it's more regarded as a local part of life and nothing shockingly shady.
When I lived in Shanghai, Beijing, Wuhan...I didn't come across a single gangster. Hong Kong and Taiwan (both of course not belonging to the Chinese mainland) on the other hand were a different ball game. In Hong Kong the organized crime groups not even try to hide. Cross the right street and you'd come across a few of them; it's like they're shunned yet almost tolerated. They won't harass you - unless you try to pick a fight in the nightlife scene of course - and sometimes they got to "collect" without any care in the world in broad daylight. They definitely got their hook in local construction rackets as well. I didn't stay in Taiwan for as long as I stayed in Hong Kong, but the situation is similar over there yet slightly more veiled.

Can't talk about Japan from a first hand experience, but a mate of mine stayed in Japan for quite a while. The "Yakuza are legal in Japan" myth is not 100% factually correct as membership of a criminal organization is officially still illegal, but they indeed are amazingly tolerated. Yakuza members are out in public and generally have little use for troubling citizens or tourists alike. The way they're entrenched in local economies is almost staggering. Tons of corporations, contractors and organizations working in finance are shaken down and influenced by Yakuza groups. Their grip seems to be as tight as can possibly get for a criminal organization in this day and age - even though it diminished a bit compared to how it used to be in the past.
Japan's an incredibly safe country with an official murder rate of 0.3 so it all seems to be a bit paradoxical; but there seems to be absolutely scary shit happening once you involve yourself with a certain crowd. And tons and tons of people in Japan go missing each year (the myth of "Japan's evaporating people"), including those with underworld connections.