Young North Korean defectors in South Korea have found success and fulfillment "I'm finally given the freedom to do things I want to do."

SEOUL, South Korea -- 12-year-old Choi Hyunmi could feel the cold hitting her chest despite her warm layers. She had been marching through curvy roads, deep woods and a frozen river for about an hour with her mother and older brother in the middle of a violent snowstorm with winds blowing in freezing temperatures.

It was December 2002 and these members of an affluent Pyongyang, North Korea, family were on their way to join Choi's businessman father on vacation -- or so Choi was told to protect their actual plan to defect.

"I did not know what I just passed through was the [North Korea-China] border," Choi, now a 29-year-old professional boxer living in South Korea, told ABC News. After meeting her father at the border, the family traveled through China, then on to Vietnam. Eventually, the family was able to settle in Seoul, South Korea.

Choi is one of many young North Korea defectors who initially had trouble adjusting to life in South Korea, but came to find success in the more progressive nation. ABC News spoke with her and two other defectors about their journeys.

Heo Jun dreamed of becoming a military commander in North Korea like his grandfather to serve "Dear Leader Kim Jong Il." But after getting caught attempting to escape to China when he was 13 in 2005, his prospects were bleak.

Besides, he could not forget what he had seen in Beijing during that attempt.

"Endless rows of tall buildings. I couldn't understand how street lights were lit all the time. And road traffic was just incomprehensible to me. It was all astonishing," Heo, now a 26-year-old student at the prestigious Seoul National University in South Korea studying political science and running a YouTube channel on North Korean defectors, told ABC News a decade after he successfully left the country.

Pak Yusung grew up watching South Korean dramas his father would bring back to North Korea from China as part of his illegal black market business -- an offense that could warrant a death sentence in the Communist nation.

When Pak was 15, his father defected to South Korea, and two years later, he sent a broker to guide Pak and his mother to follow suit. They crossed the border into China by bribing soldiers, met with other refugees and traveled south, passing the borders into Laos, then Thailand, before making it to South Korea.

"My grandfather made a mistake on his speech so he had to go to the political prisoner camp. My dad is not a member of the Communist Party, so my future path was limited, and I likely [would have become] a laborer," Pak, now 27 and a documentary producer and freelance reporter, told ABC News.

Since 1998, 32,147 North Koreans have arrived in South Korea, according to South Korea's Ministry of Unification. About three-quarters of those (73.1 percent) are under the age of 39. Choi, Heo and Pak, like other young North Korean defectors in South Korea, have found relief and liberation in their new home, where they have control over their destinies.

When they first arrive with stories of life-threatening journeys, however, they sometimes face discrimination against North Koreans in the South, where people have grown increasingly apathetic to any prospects of reunification.

Meanwhile, the two countries' societal cultures and educational systems have drifted apart so much that the disparity is evidently felt in everyday aspects of life, such as using credit cards, choosing a pizza flavor or reading signboards.

The most difficult challenge of daily life in South Korea for Choi, Heo and Park was having to learn English. The two Koreas speak the same language (with different dialects, but fairly close), but the extensive use of English words in the South is a surprising hindrance to the defectors, who took mandatory Russian classes in the North's education system.

Pak quickly realized he could not get away with only Korean and Russian if he were to achieve his dreams of becoming a filmmaker.

"I went to university to major in film, and all my classes were in English," he told ABC News. To catch up, Pak took a year off to improve his English in Dallas, Texas.

Reality in a new school was harsher for Choi, who arrived in Seoul as a preteen. Because of language differences, she did not immediately realize her classmates were making fun of her background and demanding her to go back. She stayed home for a week after finding out she was a laughing stock.

"I asked myself, 'Why am I here?'" she told ABC News. She put her "thinking cap" on for that week -- paired with her "competitive spirit" -- to figure out in which areas she was better than her new classmates. She quickly remembered, her prowess was in boxing.

In Pyongyang, Choi was picked by the Kim Chol Ju University of Education at the age of 11 to be trained in a state elite system with 19 other young boxers with a goal to "get a gold medal in the 2008 Beijing Olympics to make General Kim Jong Il happy," she said.

The girls sparred once a month and received monthly wages and food distributions based on their results.

"My family was not in need of rations, but other friends there were breadwinners from rural parts. Their parents were poor and very hungry," Choi told ABC News.

"It was a matter of survival," she said, as the bottom-ranked girls were expelled every six months. "Those friends became 19 enemies."

Even so, it was that early training as an athlete that kept her mentally strong, she said. And while boxing was "survival" in North Korea, in the South, she found it liberating to be able to follow her own training and career path.

"If you don't want to train, you can quit. If you want to, then you could go back," she said.

Choi's first match after defection was at age 18, when she become the World Boxing Association women's super featherweight champion. She has not lost a single match since then through 17 games, holding onto the champion title for the past 11 years.

Choi continues to train for a prospective match in Las Vegas in the near future and attends Korea University to finish up a master's degree in physical education.

Such freedom of choice is also what drives Heo to wake up every morning in gratitude. The best he would have been in North Korea was a farm worker, which is not what he wanted, he said.

Instead, he enjoys his life in South Korea studying political science, interacting with people from around the world on social media, and dating his South Korean girlfriend.

A quick learner, Heo started his own YouTube channel in November 2018 with a "free hug campaign" in hopes of bridging the gap between South and North Koreans. It now has over 47,000 subscribers.

"I felt there is a high emotional wall between them. Some think of North Korean defectors as spies ... so I had that thought to uploaded videos on YouTube to improve the understanding [of defectors]," said Heo. "Just eight years ago, I felt like I was 8 meters closer to the verge of death, but now, it seems like I'm 8 meters closer to heaven. The difference is that stark. I'm finally given the freedom to do things I want to do, have a choice, see things I want to see, and say what I want to say."

ABC News' Hakyung Kate Lee, Hansol Park, Sorah Choi, Soohyun Kim, Liz Sunwoo Kim and Alexandra Svokos contributed to this report.