Actor Kang Ha-na plays a Korean factory worker working at a spinning mill in Osaka during the 1910-45 Japanese occupation of Korea in the documentary film "A Song of Korean Factory Girls." Courtesy of Cinema Dal

It is well known that many Koreans were forcibly conscripted and worked as sex slaves during the 1910-45 Japanese occupation of Korea. However, the story of around 30,000 Korean women who worked at spinning mills over 40 years from 1910 in Osaka is not widely known.

To shed light on lesser-known figures, "A Song of Korean Factory Girls," an upcoming documentary film, tells the story of the women who endured a time of discrimination yet demonstrated great perseverance in an unfamiliar place.

The film vividly recreates the memories of these workers — more than 80 percent of whom were teenage girls — who crossed the sea to work in spinning mills and support their families during the Japanese colonial era. It does so through survivors' testimonies, historical records and actors' reenactments.

However, the tone of the film portrays these workers as independent, strong women who have carved out their own lives, not simply just as victims of discrimination and violence.

Shin Nam-sook, in her 90s, recalls her memories of working in an Osaka spinning mill as a teenager in the documentary film "A Song of Korean Factory Girls." Courtesy of Cinema Dal

They chose to work in Japan, drawn by the promise of a monthly pay of 20 yen ($0.13). However, they faced harsh conditions: 12-hour shifts, beatings from supervisors if threads broke and confinement behind a high fence to prevent escape from the dormitory.

Also, lacking money to buy food, they had to roast and eat pig intestines from butcher shops and endure contempt from the Japanese people.

Despite their circumstances, these women opened night schools to study Korean and went on strike to protest against the unfair treatment. They even fought for Japanese colleagues who were unjustly fired.

"There was discrimination and various incidents. But now I don't hold those things in my heart. It's the life I've lived until now," Shin Nam-sook, now in her 90s, a former worker at the spinning mill, said in the film.

Director Lee Won-sik of "A Song of Korean Factory Girls" speaks during a press conference at a theater in Seoul, Tuesday. Courtesy of Cinema Dal

Lee Won-sik, director of the film said he became curious about them after seeing the spinning mill wall during a visit to Osaka, which led to the film's production.

"When I visited Osaka in 2017, I became curious after seeing an old red wall with cross-shaped fixtures. I found it was the wall of a spinning mill, and the cross shapes were frames used to wrap wire to prevent the workers from escaping," Lee said during a press conference at a movie theater in Seoul, Tuesday.

"While the forced conscription of Koreans and sex slaves during World War II are well known, the case of the female workers seems to be less known and less researched as it's a history at the civilian level."

Actor Kang Ha-na touches the remaining red wall of a spinning mill in Osaka in the documentary film "A Song of Korean Factory Girls." Courtesy of Cinema Dal

Actor Kang Ha-na took on the lead role in the film, bringing to life the story of factory workers based on their testimonies. As a fourth-generation Korean Japanese, Kang said she received positive energy from these women while filming.

"I received positive energy while participating in this film. The lives of Korean women workers are not just about painful history. (The audience) will be able to gain bright, strong and positive energy," she said. "I felt that living proudly as a Korean Japanese is the same whether it's the first or fourth generation. I also gained energy as a Korean Japanese while filming."

Kang also played a main role in the 2016 film "Spirits' Homecoming," which dealt with Korean women forced into sexual slavery by Japan during wartime.

When asked about the differences between this film and the 2016 one, Kang said, "It was difficult when filming 'Spirits' Homecoming.' Partly because I was in the third year of middle school at that time, but I acted out a very painful and difficult history. This time, although the situations were equally difficult, I filmed thinking that they surely had bright moments too."

"A Song of Korean Factory Girls" will hit theaters on Aug. 7.