AS A POLITICAL spectacle, Sunday's Japanese election would have been remarkable anywhere, but it was especially striking in a country where politics tends to be as thrilling as plain rice. After losing a key vote on economic reform a month ago, Prime Minister Junichiro Koizumi, who is known in Japan as "Lion Heart," called a snap election, took the unprecedented step of booting 37 anti-reform lawmakers out of his Liberal Democratic Party, and appealed directly to the people. Having gone into the election with just 212 seats out of 480 in the lower house of parliament, the Liberal Democrats emerged with 296. A country whose government has traditionally been controlled by faceless faction bosses seemed suddenly democratic, even populist. Mr. Koizumi swept the election thanks to his film-star looks, his skill in fielding a team of candidates that included many telegenic women and the sheer gutsiness of his political gamble.

Yet it's not clear how much Japan's long-term project of fostering competitive, pluralistic politics will benefit. On the plus side, Mr. Koizumi has demonstrated that electoral appeal can trump the vested interests represented by his party's factions; it would be nice to believe that this boosts the political value of ideas and policies, though the main boost is clearly to the political value of image. On the negative side, Mr. Koizumi is to retire in a year, and the factions may reassert themselves. Moreover, Sunday's election delivered a huge blow to the opposition Democratic Party, which had gradually been emerging as a plausible rival to the Liberal Democrats. There's a risk that Japan will now revert to de facto one-party politics.

The prospects for economic reform are similarly uncertain. Mr. Koizumi is almost certain to jam through postal-savings reform, the blocking of which was the trigger for Sunday's election. The postal system is the world's largest financial institution and a pillar of Japan's postwar economic order; its 24,700 branches have vacuumed up a quarter of the nation's household savings, much of which have traditionally been channeled into pork-barrel projects that get Liberal Democratic stalwarts elected. Abolishing this wasteful system would be a big step forward, and it's not surprising that Japan's stock market liked Mr. Koizumi's victory. But the prime minister's proposed reform would change the postal system only gradually. Whether he will tackle other economic challenges, including Japan's health and pension systems, is anybody's guess.

Finally, it's possible that Sunday's election heralds greater Japanese military assertiveness, which the United States should view with mixed feelings. Mr. Koizumi has already reinterpreted Japan's pacifist constitution to allow for the deployment of non-lethal troops in Iraq. He has effectively scrapped the long-standing ban on arms exports by taking part in the Bush administration's effort to develop missile defense and has taken a tough stance against China's military buildup. By themselves, these policies would be welcome; given the size of its economy, Japan should make a larger contribution to global and regional security. But Mr. Koizumi has simultaneously refused to back away from the symbols of Japan's aggression in the 1930s and 1940s -- a refusal that renders Japan's new assertiveness troubling in the eyes of its neighbors, especially China. It's one thing for Mr. Koizumi to gamble flamboyantly in politics. It's another to gamble with the uneasy balance in one of the world's tensest regions.