Prime Minister Junichiro Koizumi hopped down from a campaign platform in a Tokyo square this week, his trademark gray mane rippling in the wind as he pumped his fists through an evening drizzle. Scores of teenagers, grandfathers and young mothers gasped, casting aside umbrellas and whipping out cell phone cameras. Electronic clicks and flashes filled the damp air along with a booming chant from a bullhorn:

"KOIzumi! KOIzumi! KOIzumi!"

"That's our prime minister!" exclaimed a drenched 16-year old boy in a white tank top and jeans who had waited over an hour in the rain to catch a glimpse of the Japanese leader. "Hang in there!" called out a seventy-ish woman, wiggling with star-struck joy and dropping all pretense of Japanese reserve.

"Koizumi's secret is no secret at all," said Isao Iijima, the prime minister's top aide for 34 years. "Some people call him a samurai, but the truth is that he has done what no other Japanese politician has. He has become a man of the people."

As Japanese voters go to the polls Sunday in what is considered the most important election in decades, the charismatic Koizumi -- who came to power four years ago with a pop-star style and looks to match -- is again wooing Japan.

The scion of a political family who started his career serving tea to his sempai, or mentor, Koizumi, 63, has broken many of the unspoken rules of Japanese politics. Engaging in publicity stunts such as dancing with the actor Richard Gere and making highly individual decisions in a country long governed by consensus politics, Koizumi has shocked, bewildered, angered and delighted people here.

Among the few prime ministers in the post-World War II era to rely on popularity rather than the support of party bosses, Koizumi is now betting the people will give him one last mandate for reform.

He has already made considerable progress, cleaning up hundreds of billions of dollars' worth of bad loans from the 1990s while presiding over the nascent recovery of the world's second-largest economy. After his purge last month of hardliners in his ruling Liberal Democratic Party (LDP), a victory on Sunday would leave him free to enact other reforms, such as privatizing the postal system, his current focus. He could then move on to longer-term goals of reducing the public debt and overhauling social security.

Many economists say those two objectives are essential to the recovery of the Japanese economy, which has been stagnant for nearly a decade and a half.

If the LDP and its allied party, New Komeito, fail to muster a majority, the LDP may be forced to surrender power for just the second time in 50 years. The country would then be run by the opposition Democratic Party, which says it will withdraw Japanese troops from Iraq and has demanded that U.S. Marines leave the island of Okinawa.

"Koizumi is breaking the mold for a Japanese prime minister," said Robert Feldman, chief economist for the investment bank Morgan Stanley in Tokyo. "He has decided he wants to change this country and is willing to do anything it takes, including sacrificing his own job and political party to do it."

The major policy issue in Sunday's election focuses on Japan's postal service. A decade ago, when Koizumi was head of the postal services agency, he advocated privatization of the system as the key to major reform. As prime minister, he made that goal the catchall policy of his tenure, arguing that it would rescue the nearly bankrupt pension system in the world's most rapidly aging nation and help shrink a bloated public sector.

Far more than a post office, the institution essentially operates as the world's largest public bank, with $3 trillion in deposits. The cache of cash has long been used by some LDP leaders as backdoor financing for pork barrel projects in their home districts. Special postmasters, whose jobs are often passed on from father to son, have functioned as off-the-books campaign aides.

Koizumi's most recent drive for reform began last month, when he staged a political coup against party figures who opposed his postal privatization bills. Koizumi made good on his vow to "change or destroy" the Liberal Democrats, forcing out party faction heads who had fought him for years. The move created what Koizumi now calls "the New LDP," echoing Prime Minister Tony Blair's declaration of a "New Labor" party in Britain.

Shizuka Kamei, one of the ousted LDP leaders, last week called Koizumi's "annihilation" of LDP opponents an approach "worse than Hitler's." But Koizumi insists his destruction of the party in the name of reform will have been worth it, even if the LDP loses in the coming election. Public opinion polls suggest his gamble might pay off.

Koizumi's popularity ratings soared following his decision to dissolve the lower house of parliament and eject the old guard. This time, political analysts note, his public support appears to stem not only from his style and promises but from his determination and deeds.

"Some people . . . call me henjin, in English, that is, 'odd' or 'eccentric,' " Koizumi wrote on his Web site. "But a foreign journalist advised me to think of the word instead as 'extraordinary.' Now, when people call me henjin, I take it as a compliment."

If the LDP wins, many say, it will be because of Koizumi's persona and revolutionary political style.

Koizumi has become this nation's first celebrity leader -- belting out a chorus of "O Sole Mio" with San Carlo di Napoli opera singers and tossing out the first pitch at a New York Yankees game. He appears to have an uncanny sense of what the people want.

With Japan feeling increasingly threatened by the rise of China and nuclear North Korea, he has pushed a nationalist agenda that would give Japan an official military again and has conducted regular visits to Tokyo's Yasukuni Shrine, which honors the nation's military dead, including World War II criminals. While infuriating former enemies such as China and the two Koreas, such visits sit well with Japan's growing right wing.

Seeing the U.S.-Japan alliance as the core of his country's future security, Koizumi has cultivated a friendship with President Bush, sending him a gift of a symbolic samurai's arrow after the Sept. 11, 2001, attacks as a talisman against terrorists.

At the same time, Koizumi has eschewed the tradition among modern Japanese leaders of seeking broad and expert counsel. He listens only to a tiny group of insiders, sources close to him say -- mostly his eldest sister, Nobuko Koizumi, and his aide Iijima, the son of a truck driver.

An aesthete who borrowed fine art from Japan's national museums to decorate the minimalist halls of the prime minister's residence, he is also a fierce adherent of sometimes harsh Japanese traditions. He is also known for impulsive action: He proposed to his former wife the day after their second date, then divorced her while she was pregnant with their third son because of disputes over her role as a politician's wife.

He has legal custody of his two elder sons and, following the custom here, has refused to let them visit their mother. He has also refused to see his youngest son, who lives with his ex-wife, avoiding the pair even at the 2001 funeral of Koizumi's mother.

Koizumi's opponents call him a calculating showman, who has latched on to postal reform as a false cure-all for Japan's far more complex problems. "Koizumi is great at manipulating the media and avoiding real debate," said Katsuya Okada, president of the Democratic Party of Japan.

An aficionado of Japanese traditional theater, Koizumi has proved himself adept at political drama worthy of the Kabuki stage. Japan has been captivated by the warring shoguns -- Koizumi against the ousted LDP old guard. Against many enemies, Koizumi has unleashed candidates known as "assassins," including several female celebrities and a young corporate raider.

Many voters who had been suffering from Koizumi fatigue, tired of his flashy promises of broad reform, are suddenly believers again -- particularly young urbanites to whom the LDP was anathema. The question for Koizumi is whether it will be enough come Sunday.

"For a while I did not believe Koizumi was up to it," said Sachiko Hattori, 37, a Tokyo truck driver. "But finally, he is taking action. I'm ready to give him another chance."

A police officer stands guard outside the ruling Liberal Democratic Party's Tokyo headquarters, where Prime Minister Junichiro Koizumi's election posters exhort: "Do not stop reforms." Japanese will vote Sunday in parliamentary elections forced when Koizumi ousted members of his own party opposed to his plans to privatize the nation's postal service.