For many in the city of Taipei and across Taiwan, it was the most hotly awaited event of the year. Tens of thousands of music fans gathered in Liberty Square on Saturday night for an extraordinary free concert which marked the 20th anniversary of Chthonic, the country’s most famous heavy metal band.

Wearing combat boots, lead singer Freddy Lim held the stage with the brand of music that has seen the Taiwanese “black metal” band dubbed the Black Sabbath of Asia.

But this was not just any gig: it was also a political rally ahead of a crucial year for Taiwan. Described as a “concert to calm the soul and defend the nation”, the event was intended to energise Taiwanese youth and gain political support for Lim’s new role – as a parliamentary candidate for the New Power party (NPP).

The party, which was formed earlier this year, emerged out of Taiwan’s 2014 Sunflower student movement and represents, said Lim, a means “to channel the energy and frustration of young activists and frustrated Taiwanese” ahead of the parliamentary elections on 16 January.

Last year, student demonstrators occupied government offices and the parliament in Taipei in protest over a new trade pact with China. The demonstrators adopted a sunflower as the symbol of their movement and this month’s elections will be a significant test of its strength.

“For the past three years, we have been playing around Europe, the US and Japan and we have only met our Taiwanese fans on protests. We felt it was now time, at this key moment in Taiwan’s politics, that we join together with our fans and get the energy going again,” said Lim. “It’s a show of how we support freedom of speech and to encourage our fans to all try their best over the coming year to change Taiwan for the better. There is a new political space and it will allow more and more young people to bring about real change in Taiwan.”

Lim at the Download Festival, Castle Donington, in June 2011.

Photograph: REX/Shutterstock

After two decades of touring the world with Chthonic – pronounced “thonic” – and several years as a human rights campaigner and chair of Taiwan’s Amnesty International, Lim now ties back his rocker’s long hair during daylight hours and wears an elegant suit. “This is the hard part,” he said of his new role, “getting really involved and committing to that. But I have been very encouraged by fans and I felt I should do more than just protest, that I should enter the political process. The band have been supportive – perhaps less supportive when they realised the songwriting was drying up a bit, but supportive again when they felt that I might actually win!”

Already the NPP has become the third party in the country, which is now facing a crucial moment over its future as an independent state. For years, Taiwan has been locked in a two-party rivalry between the pro-China ruling Kuomintang (KMT) and the Democratic Progressive party (DPP), which is pushing to maintain de facto independence. Since coming to power in 2008, the KMT under Ma Ying-Jeou has steered Taiwan ever closer to Beijing, to the dismay of many Taiwanese – particularly the younger generation, who fear increased restrictions on their freedoms.

“We are a free market, a free country. There is no censorship on our music: you can promote any act in Taiwan,” said Lim, whose own band is one of many acts banned from playing in China.

“But there is a strong feeling of alienation, and people feel that the political decisions which are being made haven’t been through any sort of democratic review process. Its not just students but a lot of citizens who feel politics have nothing to do with them. It is being decided by the president that China and Taiwan will come closer together – against people’s will.

“They don’t necessarily want to be estranged from China, but they do want to exist as different entities. Four years ago, president Ma Ying-Jeou said he would never meet with the president of China, then he is there, shaking his hand, and without any consideration of the people’s feelings. The people of Taiwan feel let down.”

Lim’s band have gained popularity through interweaving Taiwanese classical music and traditional instruments, as well as language, into their music and through lyrics which often incorporate national folklore.

China has claimed sovereignty over Taiwan since the end of the Chinese civil war in 1949 when, as the Communists swept to power, the defeated Nationalist government fled to the island.

China insists that other nations cannot have official relations with both countries at once, which has led to the diplomatic isolation of Taiwan. However, Taiwan has firm links with the US, from which it buys a great deal of its arms.

Despite China’s efforts to blackball the country, Taiwan has become one of Asia’s big success stories as one of the world’s top producers of computer technology.

Whether Lim wins his seart in the election or not next month, he may need to hang on to the suit: in order to crowdfund this weekend’s free concert, Chthonic have already auctioned off their stage costumes, which will be sent out – unwashed – to the keenest of their fans.