Three girls were crying on the stage. From excitement, relief and satisfaction, and over the bittersweet memories from the past few years.

It was July 2015, the final stage of the Korean reality TV show "Sixteen," where 16 young female trainees from JYP Entertainment, one of the biggest talent agencies in Korea, vying for a place in a newly manufactured girl band named TWICE.

From left, Momo Hirai, Mina Myoui and Sana Minatozaki

When the final seven survivors were revealed, it became evident that Momo Hirai was not on the winning side. This 18-year-old trainee from Japan, eliminated in the sixth episode, was only there to celebrate the winners. Her show was apparently over.
 
But it wasn't the end of the night until Park Jin-young, the chief producer of JYP, broke the unexpected news. "I, after careful consideration and much thought, have chosen two extra members to make TWICE a perfect band."

Park's announcement shocked the viewers. Two lucky girls were all foreigners; Chou Tzuyu, a 17-year-old trainee from Taiwan, and Momo Hirai, the Japanese dropout.

Since there already were two other Japanese winners – Sana Minatozaki and Mina Myoui – this decision would make TWICE a band of nine whose four members are foreigners.

No K-pop band ever had so many international talents before. Moreover, three of them were from Japan – Korea's geopolitical rival with a long, troubled history. For ardent nationalists on either side of the water, it could be a red rag to a bull.

The three Japanese girls joined on stage and burst into tears. "Honestly, I did not like this show so much," said Sana. "It was extremely stressful to see other trainees drop out. Momo was the most qualified one among us and her elimination just broke my heart. Now I am more than happy that we're going to debut together."

Two-and-a-half years later, the three girls and their teammates in TWICE are arguably the busiest and most celebrated stars in Korea.

TWICE's singles and compilation albums have been big hits both in Korea and Japan, with more than 2 million copies sold in total. Their music videos, including Cheer up, TT, Likey, Candy Pop and What is Love, racked up a combined 2 billion views on YouTube. They have been performing for tens of thousands of K-pop fans all over the world – in Los Angeles, Singapore, Bangkok, and Tokyo.

No doubt the three Japanese girls have been at the heart of this success. "A sense of homogeneity is important for fans to feel connected with the stars," said Park in an interview with Japanese broadcaster NHK. "It gets stronger when they can share the same culture and language. I think the Japanese members of TWICE worked this way with Japanese fans. We will see more cases like this in other parts of the world."

It also reflects the changing landscape of Asian pop culture. "Among the young generation a globalized, borderless lifestyle is becoming the norm. They are open to foreign cultures and able to disassociate their everyday life from geopolitical issues," said an academic at Seoul National University. "In some aspects, Korean and Japanese youngsters have more in common than they have with their older generations. This phenomenon is closely connected to the recent social changes in Asia like social media."

This is the story of the three Japanese girls who climbed all the way to the top of K-pop industry. Once humble fans of K-pop, they are now among the most adored celebrities in Asia.

It is at the same time the story of K-pop industry transforming itself. Japanese idol stars in Korea were simply unthinkable a few years ago, but the globalization of K-pop has changed its landscape and its nature as well.

More and more talents are coming to Korea to become stars, and the K-pop industry is evolving into a platform for the global entertainment market.

The three girls' story began some six years ago in Kansai, Japan. Momo was a teenage dancer from Kyotanabe, a suburb of Kyoto. Sana, a junior high schooler in Osaka, was dreaming of a pop star. And Mina was a young ballerina from Kobe.

All of these cities are, intriguingly, within an hour's radius. "It does not seem coincidental that they are all from the same region, which has long been the hub of Japanese history and culture. Kansai is the place where the Japanese arts and musical performances began and flourished. People of Kansai are also famous for their own culture – regional dialects, exquisite food, and most of all, a unique attitude to life. Comparing to other Japanese, they are outgoing, humorous, enterprising, and more open to new things," said Japan expert Choi Won-suk, the chief editor of Economy Chosun.

These features made Kansai one of the favorite destinations for international tourists. More than 10 million foreigners visited Kansai in 2016, half of all foreign visitors to the island country. It was a right environment for any genre of international pop culture to thrive there.

K-pop was not an exception. "When I went to a nightclub in Osaka, I was surprised to hear so many K-pop beats. And everyone there was enjoying them. It was awesome," said Lim Mi-jin, an office manager in Seoul.

But even in Kansai, the K-pop boom would not have been possible if it were not for the Internet, which has always been a crucial part of it. Between 2008 and 2012, when the Korean Wave was flooding Japan, broadband Internet services became widely available in Japan, and smartphone penetration surged at the same time.

Social media and video sharing platforms followed this change, emerging as the major channel of consuming pop music. The Internet gave Japanese teenagers virtually unlimited access to international pop culture, and K-pop was one of the biggest beneficiaries. Bands like Kara, Girls' Generation, Big Bang, 2NE1 and 2PM quickly became their idols.

Many K-pop cover groups organized. They learned the dances from video clips online. Some K-pop bands released "dance practice" or "mirrored" versions of their music videos to help their fans learn their moves.

"Technologies like smartphones are breaking down the language barriers. We used to listen to American pop music and bought the CDs with little knowledge of English. I think youngsters nowadays are enjoying K-pop in the same way, regardless of language," music journalist Masayuki Furuya told NHK. "More and more people are consuming music via video clips. The visual aspect is getting more important than the music itself. Otherwise, K-pop would not be this popular."

Momo had been a K-pop fan since was a little girl. "I was fascinated by the powerful yet precise dance performances of K-pop. I loved Rain and 2NE1. I always wanted to thrill people with my dance, and K-pop dance thrilled me," she said in an interview.

Influenced by her sister Hana Hirai, she began dancing at the age of three at a dance studio in Osaka. "Japanese pop legend Namie Amuro was my idol. I wanted to be like her someday," said Momo.

Mina's K-pop experience began with K-pop dances. "One of my friends in middle school asked me to join her K-pop cover group. I remember that the first dance we did was one of Girls' Generation's. Later I went to K-pop concerts by the bands like Big Bang and CNBLUE. I was deeply impressed by their performances."

Unlike other K-pop fans, she was not satisfied with remaining a fan. She signed up for a dance studio near her school to learn K-pop dances.

For Sana, K-pop was a new horizon beyond Japanese pop. "My dream at first was to be a singer in Japan. But observing the K-pop boom around the world, I realized that K-pop singers have a lot more opportunities, not only in Asia but also globally."

Sana's favorite K-pop bands were Kara and Girls' Generation. In 2009 she joined EXPG, a franchise talent agency in Osaka, and trained there until 2012. As early as 2011 she tweeted, "I've got interested in Korea. I want to go there."