JAKARTA — Siti, Widi and Firdda are petite. But the sound of their band, Voice of Baceprot is huge. When I met them, the three girls were dressed entirely in black: from headscarves to sneakers. The tips of their fingers blue and scratched from hours spent practicing guitar.

This is their first time in a radio studio. They cling to each other. Widi is 15 and the youngest, and she giggles and shies away, hiding behind the others. Today they're getting ready to play alongside Superman is Dead, one of Indonesia's biggest bands, in front of an audience of several thousands. They're nervous.

The young band has had a rapid rise to fame. So much so that they tell me they're reading books on emotional intelligence to try and stay balanced throughout the head spinning experience. Singer Firdda Kurnia is 16 years old, and as the oldest of the three, she's become spokeswoman. She says it hasn't been a smooth ride.

Some people slander and hate us

"At first, our closest family members didn't support us," she told me. "Because maybe they didn't know what we were doing. And this music is always identified with promiscuity. But once they knew what we're doing, what our activities are like, they started to support us."

Every day after school, the girls meet and practice for three hours. And their dedication is paying off. Voice of Baceprot has fans across Indonesia and around the world, from the UK to Australia.

But it's not only fans that have noticed them. The band has plenty of loud and aggressive critics threatening them — both at home, and on social media.

"There are some people who hate and slander us," Firdda says. "They say metal is inappropriate and it's inconsistent with us wearing the hijab, because metal is considered dark music, satanic music. But through our songs, we can prove that we can play metal music without abandoning our responsibilities as Muslim women, who have to cover our bodies."

Some metal music is nihilistic and dark. That's the music that the three girls fell in love with when they first heard it. And they've learned a lot from metal bands like Slipknot, Metallica, and System of a Down, including how to use music as a means to express social commentary.

But unlike others, Voice of Baceprot is unapologetically idealistic. With intolerance on the rise in Indonesia, their message is one of hope.

They have four original songs, and Firdda told me about one of them. "It's called ‘What's the holy today,"" she said. "These days more people feel that they're right. Everyone else is wrong. A sense of egoism. It's become hard to find tolerance," she continued. "So through that song, we want to make a statement about peace and tolerance."

When they're not playing music, the three girls are finishing their final years of school. They're at a secretarial school. But they tell me that's not the future they're hoping for.

They'd prefer use their fingers playing guitar rather than from typing memos. So they're setting their sights big. "First we want to make an album that can be published in Indonesia and abroad. We also want to perform abroad in the UK, big festivals abroad, America, Australia, a lot of countries," Firdda said.

She says they're determined to keep doing what they love. And they've got a message for other women. "Do not be afraid to be different. Stay confident, look different, voice your idealism and keep your idealism."

Firdda has one more message aimed at women of her own faith. "And of course, Muslim women today are underestimated. We want to break that perception. Muslim women like us can also work and have ideals and no one can stop that."