TOKYO -- In April, Nike erected a billboard in front of the Apple Store in Shibuya depicting a brakeless track bike and the slogan, "No Brakes, No Problem."

Immediately, a furious discussion started up on the bicycle board of 2-channel, Japan's biggest and most important internet forum. Forum members soon launched a massive phone campaign targeting Nike, the Tokyo police department and the Bureau of Economy, Trade and Industry. Very politely, the mob lectured officials about the dangers of speeding downhill without brakes. Less than 48 hours later, the billboard was taken down.

The 2-channel forum is a Japanese internet phenomenon. This single site has more influence on Japanese popular opinion than the prime minister, the emperor and the traditional media combined. On one level, it serves as a fun, informative place for people to read product reviews, download software and compare everything from the size of their poop to quiz show answers. But conversations hosted here have also influenced stock prices, rallied support for philanthropic causes, organized massive synchronized dance routines, prevented terrorism and driven people to their deathbeds.

"2-channel stirs the naked heroism that lives in every individual," says Kensuke Suzuki, the author of several books on Japanese internet culture. "This can be dangerous, but in a community where you can't ordinarily express your true feelings because of its restrictions, it's really important."

The 2-channel community is an anonymous anarchy, and for the Japanese it is refreshing liberation from their strict, button-down lives. The forum's origins trace back to a college apartment in Arkansas, where founder Hiroyuki Nishimura was a student in May 1999. While most extant bulletin board systems were themed around certain topics of interest, Nishimura created a comprehensive forum that branches off in multiple tangential threads, making its growth exponential. 2-channel operates without moderation; some users simply volunteer to be "deleters," removing posts that don't fit the lax guidelines.

"On 2-channel, there's a culture of self-determination that doesn't exist elsewhere," says Daisuke Okabe, a research associate in new media technologies at Keio University. "It's widely acknowledged as a special place on the internet, where people can combat the mass media on a grass-roots level."

In Japan, speaking out risks public humiliation, so many don't. But on 2-channel, citizens can criticize politicians and celebrities, children can bitch about their parents and students can rat out their teachers. "I know that if I say something stupid in class, it'll probably be on 2-channel later that day," Okabe says. "Inevitably, I sometimes find myself censoring myself because of that."

Initially, 2-channel was hosted on a single set of servers owned and operated by Nishimura. Two years later, the forum had grown so big, he ran out of money. Fearing its annihilation, a team of programmers on the Unix board saved the server by devising a read.cgi code and installing a proprietary browser. To cover costs, Nishimura started charging an annual membership fee of $33 for access to the archives. Spam filters and IP logs began a year later.

Today, with 2.5 million posts a day and about 800 active boards split into thousands of threads, 2-channel is the biggest BBS in the world. And while the posts on 2-channel are often nothing more than ramblings of the average Joe, its scope is so widespread and its threads so influential that companies and authorities monitor it closely.

Dentsu, the world's biggest ad agency, has a "buzz research" division that monitors 2-channel constantly to see what people are talking about, and there are several consultancies that advise companies on managing their online reps.

Even government officials are stepping into 2-channel forums to solve crime. After a bus hijacking and murder was discussed in 2000, police started monitoring the boards for leads and tips. So many arrests were made in the following months that posters stopped publicizing their desire to kill their infuriating parents or destroy their school, says Suzuki.

But like most web communities, 2-channel has its share of problems. On occasion, the 2-channel community behaves like a mob, turning on members who transgress with massive amounts of hate mail, the revelation of private information and stalkers monitoring their homes 24/7.

"It's very yakuza, in a way," says Suzuki. "An angry, riled up 2-channel community has no sense of responsibility and will do anything to break its target."

Currently, its 30-year-old founder faces charges in more than 50 civil lawsuits in Tokyo alone and more than $4 million in settlements and court penalties for libel, defamation, copyright violations, privacy and personal injury. But Nakamura is defiant. "I don't have any intention of paying up to a country whose laws I don't respect," he told Yomiuri Shimbun, a major Japanese newspaper, last month. "As long as they're not handing me the death sentence, I'm not backing down."

2-Channel in the News:

Love: One of the most famous 2-channel stories is that of Train Man, a romantic tale about a socially awkward geek who finds true love with a beautiful woman by following the advice of his online friends. Train Man's 2-channel conversation threads were compiled into a book, which led to a manga series and ultimately a movie that premiered in the United States late last year.

Philanthropy: In October 2004, thousands of people on one of the volunteer boards rallied help for victims of the Niigata Prefecture Chuetsu earthquake. And when a thousand folded cranes at the Hiroshima Atomic Bomb Memorial were burned to a crisp, a single call for help on 2-channel yielded 830,000 newly folded cranes in a matter of days.

Mass suicide: Last December, an anonymous post began a thread with this simple message: "28 years has been enough. I live in Hiroshima. I plan to die within the month. Will somebody come with me? I don't have the courage to go alone."

More than 700 messages follow. "Take a nap," one says. "What's wrong?" another asks. "My college girlfriend was gang-raped, and she killed herself. Plus I have over 4 million yen in debt," the guy responds before disappearing completely from the forum. What happened to him isn't known, but the conversation continues among other suicidal hopefuls, self-hater-haters and gentle negotiators. The last post, published just a few hours ago, is a goodbye note by a woman who betrayed her lover. The conversation is one of many mass-suicide discussion threads.

Stock market: On Dec. 8, 2005, at 9:27 a.m., a trader for Mizuho Securities mistakenly placed a sell order of 610,000 shares for 1 yen instead of 1 share for 610,000 yen for the recruitment agency J-Com. Word instantly got out on 2-channel that a mistake had been made, and two twenty-somethings became millionaires overnight. Mizuho Securities is suing the Tokyo Stock Exchange for 40 billion yen in losses, citing a glitch in the exchange's system that caused a delay in the cancellation order.

Crime: On May 3, 2000, a 17-year-old boy who called himself Neomugicha ("Barley Tea") posted a strange warning message on 2-channel an hour before hijacking a bus in Fukuoka and killing one passenger. 2-channel regulars who had earlier ignored Neomugicha's claims started paying serious attention to unusual threats. So did the police. A copycat who called himself Neomugishu ("Barley Wine") was later arrested after he boasted of a planned terrorist attack on a railway company.

Vote rigging: When comedian Masashi Tashiro was nominated for Time magazine's Person of the Year in 2001, 2-channelers hacked the voting system and placed multiple votes that propelled him to the No. 1 position over Osama bin Laden and George W. Bush, and crashed Time.com's server. Tashiro -- who is infamous for his blatant sexual harassment and belligerent public behavior -- was removed from the list.