In an ideal society, various branches of the state interact to put criminals behind bars. Talk to those involved in law enforcement, though, and most will say there's only so much they can do without the cooperation of private citizens.
That's where Masaru Jo comes in.
Jo used to be an insurance-company salaryman. These days, though, he's the director of the Kabukicho Shotengai Shinko Kumiai (Kabukicho Shopping Center Promotion Association) and can read chapter and verse on every extortion scam and illegal enterprise Japanese gangsters use to make money.