With revising the pacifist Constitution rapidly emerging as the primary issue in the upcoming Upper House election, proponents and opponents of change alike used Friday — Constitution Day — to press their cases.

A group in favor of changing the Constitution held a major rally in Tokyo while thousands of its defenders held a protest march through the capital.

In the 66 years since its promulgation, the constitutional debate has rarely been this vigorous. The debate heated up after the Liberal Democratic Party took back control of the government in December, with Prime Minister Shinzo Abe looking to make it a focus of the Upper House campaign this summer.

His backers expressed hope Friday Abe will achieve what they have dreamed about for decades.

"A lot of prime ministers through history clearly stated at the start of their tenure that they wouldn't touch the Constitution. . . . But Prime Minister Abe's Cabinet has already made pretty clear its intention to embark on amendment," said Junpei Kiyohara, a representative of a Tokyo-based organization founded by late former Prime Minister Nobusuke Kishi that favors changing the national charter.

About 450 people attended its annual gathering in Shinjuku Ward on Friday.

Kiyohara said recent media polls have suggested the majority of the public support the idea of constitutional revision.

Because the current Constitution was drafted by the U.S.-led Allies, Japan has still not established its complete independence from the United States, he said.

He also said revising pacifist Article 9 is crucial, saying it is responsible for China's increasing pressure to undermine Japan's sovereignty over the disputed Senkaku Islands as its renunciation of war frees foreign aggressors of any fear of retaliation.

Kiyohara echoed Abe in saying that the first step should be to water down Article 96, which states that constitutional amendments must pass both Diet chambers with a two-thirds majority and be put before the public in a national referendum.

With the forces for amendment increasing their presence in the Diet, defenders of the Constitution in its present form exhibited a sense of crisis Friday, saying the charter is in danger.

"It's been about six months since the general election (in December). The situation regarding the Constitution has been greatly changed" by Abe's Cabinet, said Ken Takada, who helped organize a rally in the Hibiya district.

Abe's intention is to make it possible for Japan to participate in wars, and this must be stopped, he said.