North Korean defectors arm themselves with the most powerful weapon they have: The truth

Roughly 35 miles from the world's most fortified border, Jung Hoon Choi led a group of 20 fellow North Korean defectors on skis up the mountains of Gangwon-do in South Korea. For them, it’s more than just a sport. It’s an act of defiance against their home country.

"We're here with a purpose: to become fit and build our boldness," Choi told ABC News' "Nightline."

And in a working class neighborhood of Seoul, a woman uses her voice on the airwaves to pierce through the border.

These people are among the estimated 30,000 North Koreans who risked their lives and defected to the south. Some are weaponizing themselves against their former government, using what they say is the truth -- the most powerful ammunition against a regime they say is built on lies.

Watch the full story on "Nightline" tonight at 12:35 a.m. ET

Defector Han Ga Hee is an announcer for Free North Korea Radio, which airs news across the border to a country where she says there is just one channel with programming about the ruling Kim dynasty.

"When they heard another defector came and is living here in a free country -- and how they talk truthfully about democracy -- it's a huge shock," she said. "Through that, it can change their views."

Han, who risked everything to cross the border, left her parents and brothers behind and likes to believe they listen to her voice when she is on the air.

Her empathy for fellow defectors and dedication to their cause stems from her own brutal story of fleeing. After her father was tortured, Han fled to China but was caught by North Korean guards. She said they performed a body cavity search on her and she was convinced that she would be killed.

"If you were wearing jeans, they would it rip it apart and hit you," she said. "If you were pregnant, they would beat the woman to cause a miscarriage."

Undeterred by her experience, Han paid smugglers to help her flee again. This time, she faced human trafficking -- what the State Department estimates could be experienced by as many as 10,000 North Korean women and girls. Last December, Han shared her experience of being sold three times as a would-be "bride" in China during a congressional hearing.

"When the traffickers sold me to a Chinese man and threatened me with a knife as I resisted, I could still have hope and survive and get to the land of freedom," she said during the hearing.

She said her perseverance came from listening to other defectors on the Free North Korea Radio broadcast.

"Listening to my fellow North Koreans speaking from Seoul to their friends and family in North Korea, my suspicion melted away and I finally decided to defect to South Korea," she said during her testimony.

There are thousands of stories of survival and freedom from those who fled a regime that has condemned as many as 120,000 of its citizens to remote prison camps.

Han served food to members of the North Korea People's Liberation Front (NKPLF), a paramilitary group composed of former North Korean soldiers that is plotting to bring Kim's empire down, saying she felt it was her responsibility to feed them well. Two in five North Koreans suffer from malnutrition, according to U.N. estimates.

"Many came here because they couldn't stand the hunger," she said. "Here, they shouldn't have to starve."

But these small acts, like sharing a meal, has also been a way for defectors to feel a sense of community in a foreign country. When Jung Hoon Choi, the commander of the NKPLF, led a group of defectors through a particular ski drill in the mountains, made possible by church donations, he wanted it to be a team building -- the joys of which provide a momentary reprieve from painful memories of fleeing, often without loved ones.

"When I see snow, all my stress fades away, and coming down from the top, you forget about everything, you only think about skiing," he said. "But, it's not about skiing by myself, [but] all together."

But Choi also understands the threats of nuclear war and he is on a mission to tell the world what he thinks of the North Korean regime.

"To reveal [their] lies is the first step to destroying the Kim Jong Un regime," he said.

Talks between North and South Korea, as well as the United States, have resurfaced in recent months. Most recently on Tuesday, South Korean national security chief Chung Eui Yong announced that after his meeting with Kim, North Korea was willing to talk to the United States to discuss denuclearization and normalizing North Korea-U.S. relations.

The North, he said, also promised not to use nuclear and conventional weapons against South Korea, and made clear it would not continue with additional nuclear experiments and ballistic missile tests.

President Trump called North Korea's reported willingness to engage in discussions with the United States a positive development, saying it would be a "great thing for the world." Trump also said that the United States was going to see whether the North Koreans were willing to give up their nuclear weapons but that the dialogue had come a long way.

The Trump administration has repeatedly said it will only engage in direct talks with North Korea if it commits to full denuclearization. On Feb. 23, the United States put new sanctions on 27 trading and shipping companies, 28 vessels and one individual for evading U.S. and U.N. embargoes on trading oil, coal and other fuel with North Korea. The administration also warned that it might even impose a military blockade to stop North Korea's nuclear and ballistic missile programs.

According to Choi, North Korea thinks fighting in winter would be to its advantage because it has fought a war in the cold before and that if North Korean leader Kim Jong Un were to declare war, he would do it during winter.

During the Korean War, "many Americans and South Koreans froze to death in the winter," Choi said, and the hermit kingdom called upon its special forces -- the ski troops -- so he wants to be ready.

When Choi fled North Korea, his brother was arrested and eventually executed in retaliation. His tears have dried, he says, but the loss motivated him to take up arms.

"When you go to your family, you can proudly [say] that you didn't just live in the south to fill your bellies, or for money," he said. "[You can say,] 'We cried for you and we fought for you.'"

But Choi says his most powerful weapon is information. USBs filled with glimpses of life outside the repressive regime -- like popular Korean dramas and K-pop -- are smuggled into the neighboring country every three months.

"[USBs] with outside information that will help change the beliefs of North Koreans," he said, holding a box full of the drives.

North Korean defector Sang Hak Park's choice of contraband is deemed so dangerous by his home country that, according to him, North Korean spies have tried to assassinate him at least twice.

Annually, he sends thousands of giant balloons filled with TV shows, movies and anti-regime leaflets.

He said these kernels of hope and truth are the best alternatives to phone calls, letters or emails that are impossible to send home.

"What a liar and hypocrite fears most is the truth," he said. "This is because the leader is idolized there, higher than God. If you destroy the idol, the dictator nation will be pulled down."

Like Choi, Park also gets round-the-clock police protection. However, the exhaustion of living under constant threat is vanquished by the larger goal.

"Someone has to do it," he said. "The defectors who know the truth consider it a mission and part of their conscience to do this."

ABC News' Lauren Effron, Alisa Wiersema, Cho Park and Hakyung Kate Lee contributed to this report.