Winning an audition is one thing. Become a star is another. New lives as cadets in a Korean entertainment mill were waiting for Sana Minatozaki, Momo Hirai, and Mina Myoui.

Sana and Momo landed in Korea in April 2012, and Mina in January 2014. Life all alone in a foreign country is tough for a teenager, and the language was the first hurdle.

Korean and Japanese are closely related and sharing many features. But differences in phonetics often perplex Japanese who want to learn Korean. Teaching languages to the trainees grew important for K-pop agencies in the late 2000s as K-pop expanded into more global markets. It also meant that more talents were coming from overseas.

From left, Mina Myoui, Momo Hirai and Sana Minatozaki when appearing at "Sixteen," a reality show aired in 2015
From left, Mina Myoui, Momo Hirai and Sana Minatozaki when appearing at "Sixteen," a reality show aired in 2015

These days trainees at major Korean talent mills are taught to speak at least two languages among Korean, English, Chinese, and Japanese. But the lessons were never enough. "Besides the lessons, I worked by myself. I watched TV shows making notes of the difficult words and expressions," said Sana. She looked up words on the internet, translated them into Japanese, memorized them, and tried to use them in everyday life.

Integrating with the other trainees was another big challenge. Cultural differences and styles often clashed in the competitive atmosphere of a trainee corps.

"You have to be very polite to your elders. It's a crucial part of Korean culture. At the same time, you are supposed to be treated equally. If a trainee is given preferential treatment due to his or her ethnicity, some other trainees can become jealous. I can't say it happened only in my company," said a former trainee in one of the biggest talent mills.

When the three girls joined JYP Entertainment, there were a few other Japanese trainees there already. Mone Fukuhara was one of them. "There was no ostracism for the Japanese trainees. Most of us maintained good relationships with the staff and other trainees," said Mone in a Q&A with her fans.

But of course the most strenuous challenge was the training itself. The K-pop industry's training system is notoriously grueling. "Training schedules are tight. Hours of singing, dancing, and language learning almost every day. Moreover, a monthly test follows. Failing means you drop out," said a former K-pop agency professional surnamed Yun who did not want to give his full name.

"Three to five years' training is the baseline. Some trainees are lucky enough to debut within a couple of years, but that's rare. When training gets longer, trainees are more likely to be exposed to psychological problems. If a trainee gives up and leaves, many agencies claim the expenses for training back. You could say that it's a long-time survival show."

Momo worked more than 10 hours a day. "Sometimes I practiced until midnight when there was only me in the building, but was a good time to practice singing," she recalled.

It took three years and seven months for Sana and Momo and a year and 10 months for Mina to debut. For Ji-hyo, the leader of TWICE, it was about 10 years because she started training at the age of eight in 2005. She had a few chances to debut earlier but luck was not on her side. "I was so distressed that I dealt with it by eating. But that made me gain weight and I lost my confidence," Ji-hyo said in an interview.

Back in 2012, four Japanese girls at JYP, including Sana and Momo, were preparing for their debut in Japan. But the deterioration of the Korean-Japanese relationship ruined it. K-pop went cold in Japan and their debut was suspended indefinitely.

Sana was regrouped as a member of 6MIX, JYP's another girl band targeting Asia. But it did not last long either. Only weeks before their debut, the ferry Sewol sank in the West Sea and more than 300 people died. Korean society mourned, and 6MIX's debut schedule was postponed and finally canceled.

JYP embarked on a new project to launch another girl band. It needed an impeccable plan and turned to a proven method -- a reality TV show. Back in 2008, JYP had already collaborated with music channel Mnet to produce a reality show to find a new boy band.

"Sixteen," the reality show in 2015 from which TWICE sprang, followed the same pattern, with an emphasis on brutal selection. They went through seven missions including two public showcases for five months. After each episode, the trainees were regrouped into two groups, the major and the minor. One member from the minor was eliminated at the end of each mission.

The intention was clear. "You never know who's going to be a superstar. The best strategy is to let the people choose them. Through this method, you can also create a powerful fan base even before the debut," said Yun. The strategy was initially developed in Japan. Participating in the selection process, people turn into fans and spend money on televoting, texting or CDs that entitle them to vote.

Sixteen started in May 2015, again in collaboration with Mnet, and sixteen trainees from JYP appeared at the show. In 10 episodes of seven missions, they were tested rigorously in every aspect of their skills, from singing and dancing to their passion, and their personalities.

Four trainees were eliminated in the first nine episodes. In the last episode of the show, they were voted in by the viewers for the final members. Only nine trainees were chosen to be TWICE. Among them were Mina, Sana, and Momo.