This is not because the book is badly researched, poorly written, or any other flaw stemming from the authors or their approach. Rather, it is depressing because the authors have done their job well, and pointed out how Japanese organized crime has survived and thrived by turn over the course of many years, and how that ultimately means that honest people have been intimidated, extorted, and otherwise robbed.
The book focuses on the 20th century, as records of underworld activity are functionally non-existant before that (the revised edition is circa 2002, so would not have had time to include data from this new millenium). Still, it's quite a story. The absolute nadir of the book is fairly early on, when the authors tell that many of the ultra-rightist gangster leaders, after making a killing in occupied China, were arrested by the US occupation, then released several years later without being brought to trial because their assistance was desired by certain occupation officials (and later CIA operatives) in strong-arming the Japanese left into submission. In other words, given the choice between ultra-rightist criminals and pacifistic democratic socialists, the Americans took the former.
That helped lead to decades of heavily influential mobsters, including some that played kingmaker for Prime Ministers. That part of the story, though it doesn't hit as close to home, was still shocking.
The book is not nearly as gruesome as I thought it might have been: there are no real descriptions of the violent beatings and the like that the Yakuza did some times inflict on their opponents.
The book ends, like so many true stories, with nothing resolved. The Yakuza have changed over time, becoming more violent and smarter, but in doing so they've lost a lot of their influence. Politicians once needed Yakuza support behind the scenes to do campaign work, but now the Yakuza's image and more thorough press and police investigations mean politicians can't afford to accept that kind of support if they want to win.
It's worth noting that the authors' background is as journalists and that does effect how they gather their information and put it together. Nothing that's a deal breaker, but something I was definitely aware of at several points, especially when they started talking about resources and methodology.
Overall, recommended. Not the best thing I've ever read, but a very good treatment of the subject, and helps frame some of the cultural exchange happening all around the Pacific Rim.