If you’re ever minded to dance the night away to trance music, or even old-fashioned rock, you may have a tough time finding a venue in Japan these days. In fact, you may end up waltzing away hours inside a police station, peeing into a cup after being rounded up in a raid. Yes, indeed, a War on Dance is raging.

On Sept. 2 in Tokyo, members of a gang called the Kanto Rengo burst into a VIP room in Roppongi’s Club Flower at 3:40 a.m. and clubbed a man to death in front of 300 people. Since then, police raids have intensified on the clubs, discos and live-music venues that make the city’s night life vibrant and fun for many.

However, the raids didn’t begin in the capital, but in Osaka earlier in 2012. Ostensibly, the clubs there — as later also in Tokyo and Fukuoka especially — were targeted for violating Japan’s archaic Adult Entertainment Laws (AELs), which forbid dancing after midnight. The police are simply enforcing the laws — at least that’s the official line.

But anyone who has lived in Japan for several years knows that wasn’t always the case. Sure, the laws existed on the book; gathering dust and rarely enforced.

So why is there now a War on Dance? Is it a part of a War on Drugs?

Who do we blame? Do we blame the police? Do we blame the Kanto Rengo crew for killing a man after dancing hours, thus reminding everyone the AELs were being ignored? The answer is complicated.

Let’s start with the obvious: Believe it or not, it really is illegal to dance after midnight in most venues in Japan. This fact was well covered last year in “Odotte wa Ikenai Kuni, Nihon (Japan: The Land Where You Can’t Dance),” a book edited by music writer Ryo Isobe. As it explains there, longstanding AELs were revised during the postwar Allied Occupation to clamp down on then-infamous “dance halls” that were thinly disguised venues of prostitution.

Now, decades on, “dance halls” have been replaced by clubs, discos and bars with dance floors; they are not proxy brothels. The places people dance have changed, as have the customers; the laws have not.

I don’t think there is anyone who would argue that dancing itself is dangerous or unhealthy. In fact it is part of the national educational curriculum in Japan. Some forms of dance are considered cultural treasures. So why would dancing at a club after midnight miraculously transform into a threat to public welfare? Do dancers morph into rampaging werewolves as the clock strikes midnight?

There is no logical answer.

One unofficial answer a senior police officer gave was: “It’s much easier to raid a dance club on violations of the AELs than it is to get a warrant for a drug search. Dance clubs are hotbeds of drug activity.”

Maybe that’s partially true. At some dance parties, there may be people using ecstasy (MDMA). Others may be getting so drunk that they get alcohol poisoning. There will also be people just dancing. Should all late-night dancing be banned because of a few reckless people?

The hardline enforcement of forgotten laws may make the police look good in some people’s eyes. It is a nuisance for everyone else. It hurts the business of legitimate clubs and discourages people from staying out late, making nightlife boring. If there’s no place to dance after midnight, many people will go home.

It’s bad for tourism, too. “Tokyo: The City That Sleeps Before Midnight” — try luring overseas visitors with that slogan.

Ultimately, though, besides stomping on a simple pleasure and hurting the economy, the police raids encourage corruption, because late-night clubs will either go out of business or pay bribes and protection money to stay off their hit lists.

That brings us to another reason for the War on Dance, which stems in part from nationwide Organized Crime Exclusionary Ordinances (OCEOs) that went into effect on Oct. 1, 2011. In the old days, the clubs paid off the local (officially designated) yakuza; in return, they often got advance notice when a token raid was coming. The yakuzas also provided muscle when customers got out of line and generally kept local street crime down: no muggings, purse-snatching or theft allowed. The smart clubs avoided getting shut down, kept pushers off the premises — and people felt safe patronizing them.

The police knew if clubs were operating way past legal hours, but enforcement was so sparse that late-night dancing existed in a comfortable gray zone.

But when the OCEOs made doing business with the yakuza a crime in itself, the clubs stopped paying them — and non-officially registered organized-crime groups, such as the Kanto Rengo, cut in on the dance. But as well as becoming unofficial security guards, they soon found the clubs were lucrative venues to peddle drugs and, in some high-end ones, prostitutes as well.

The “dance hall” days were here again, and the Club Flower killing made it clear that the “new yakuza” were now running the nightlife. The investigative journalist Atsushi Mizoguchi coined a term for these outlaws: hangure. It comes from han (half), and gurentai — undisciplined youth gangs in the chaotic postwar period who preyed on the general population, engaging in theft, robbery and violent crimes. The “half” in the term is also a nod to the fact these new groups are half-yakuza, as many are backed by yakuza or ex-yakuza who can no longer operate in the open — and so have no code of honor to burden them.

Within weeks of the Club Flower murder, the National Police Agency reportedly issued a directive to all police departments to strictly enforce the AELs. The directive was meant to hurt the hangure and deflect criticism of lax enforcement. And the cops have been doing their jobs.

Japanese police are no longer comfortable with gray zones — or seemingly with “half-gray” ones, as that’s another meaning of hangure; everything has to be black and white. Gray is the enemy and dance-club closings are the casualties of a badly run war.

Not everyone is taking this haphazard enforcement lying down. The Let’s Dance Committee, headed by a lawyer and run by volunteers, is lobbying for changes in the law that will protect Japan’s “dance culture.” They have already collected more than 150,000 signatures for a petition to the government.

But in the meantime, until someone brings the laws up to date, the War on Dance will keep on moving to the music of the National Police Agency marching band.

Investigative journalist Jake Adelstein is the author of “Tokyo Vice,” a board member of Polaris Project Japan and a contributor to The Atlantic Wire and japansubculture.com. His email address is jakeadelstein@me.com.