How do pop stars take their first steps into the entertainment industry? For Sana Minatozaki and Mina Myoui of TWICE it was "street casting."

"Professional recruiters roam the streets looking for talents. Sometimes they visit concert venues where many K-pop fans are," said a former K-pop agency professional surnamed Yun who did not want to give his full name. "If a stranger comes up to you and offers you an audition, you may well think he or she is a crook. But it's still one of the best ways to pick up real talents. You need to dig into the dirt to find a jewel."

Sana ran into a JYP Entertainment professional while shopping with her friends. "I was there to buy a birthday present for a friend. Suddenly a stranger who spoke Korean came up to me and asked me if I'd heard about JYP."

A third grader in middle school, she did not know anything about the Korean company. To appease her suspicions, the recruiter showed her a few pictures of JYP singers including Ok Taec-yeon and Su-zy. Sana immediately recognized them as stars from "Dream High," her favorite Korean TV show at that time. She took the audition next day.

From left, Momo Hirai, Sana Minatozaki and Mina Myoui

Mina has a similar story. "I was shopping with mom in Osaka when a JYP recruiter came up to us. He offered me an audition in Japan, saying it was the last day. I was delighted but also very embarrassed. Everything was all too sudden," she told an interviewer.

Unlike the others, Momo Hirai already had some experience of the K-pop industry. In 2008, she took part in a K-pop music video for singer LEXY with two friends. She also appeared on the Korean audition show "Superstar K" in 2011. It was the following year when a Korean scout contacted her. "He saw the YouTube video of me dancing on stage, and he offered me and my sister Hana an audition in Tokyo and I took it."

The big three K-pop entertainment agencies -- JYP, SM and YG -- have experience of debuting international talents and are also known to offer a relatively good environment for foreign trainees. But that did not mean that all of the three girls, in their mid-teens and speaking no Korean, would make it through the tough training and debut successfully.

The parents of the three girls trusted the dreams of their children. After Sana passed the audition, her mother took her to a concert of 2PM. "On the way back home, she asked me 'what did you feel?' and I told her 'I want to be just like them.' That was it. They let me go ahead," said Sana in an interview. "We knew that I might not be able to debut in Korea, but even if that was the case, it could be a good life experience."

Mina faced the worries of her parents. "They didn't like my idea at first. Going abroad, quitting school, and giving up the ballet I'd studied for 11 years; they were worried about all of these. I could do nothing but keep telling them 'It's my dream. I must go to Korea.'"

She had had a few auditions in Japan before, none of them very successful. "I got another chance with JYP, and I wanted to grab it," she recalled. Her parents finally let her go, impressed by her passion.

Momo and her sister's audition in Tokyo went unexpectedly. Only Momo passed. "I didn't know what to do. Then my dad told me 'You do what you've got to do.' My dance teacher also advised me to go to Korea," said Momo.

That was the moment of truth for her. Momo's parents already knew that their kids were talented dancers. "Until then, I'd always depended on others. I thought it was time to believe more in myself, so I decided to go to Korea."