When Chinese director Guo Ke made his first short documentary about "comfort women" -- women forced into sexual slavery by the Japanese army during WWII -- in 2012, he named it "Thirty Two," the number of known survivors on the Chinese mainland.
When he started a follow up documentary on the same issue two years later, that number had dropped to 22, which became the name of the second documentary, released on August 14 this year.
In contrast to the decreasing number of survivors, Chinese moviegoers are showing increased awareness of their suffering.
Box office revenue for "Twenty Two" exceeded 10 million yuan (1.5 million U.S. dollars) on its first day, and 100 million yuan within one week, making it the most successful documentary release in China.
According to China Film News, as of Aug. 27, the film had made over 160 million yuan in total and ranked the seventh in last week's box office earnings.
It scored 8.9 out of 10 points on Douban, a popular Chinese movie rating platform, higher than 80 percent of its peers in the documentary film category.
Guo attributed the unexpected success of his documentary to the audience finally paying attention to the history and traumatic experiences of this group of women. He has promised to donate all his personal profit from the film to the Research Center for Comfort Women at Shanghai Normal University.
Across Asia some 400,000 women were forced to be sex slaves for the Japanese army during WWII, and nearly half of them were Chinese, according to the center's research.
It is estimated that 300,000 of these women died as a result of this atrocity.
When Twenty Two debuted last month, the number of known survivors had dropped to no more than 20, although there are undoubtedly many more who have not admitted to being survivors due to the shame of what they went through.
According to Su Zhiliang, director of the research center and the advisor for Guo's film, the oldest known survivor is now 97 years old and the youngest is already 89.
"They will soon all be gone," Su said, describing the task of locating the remaining survivors and collecting evidence of their tragic experiences as a "race against time."
Twenty Two was not originally expected to be a box office success. Few people believed the documentary could make money, Guo said he had even considered selling his house to finance the production.
At that crucial stage, actress Zhang Xinyi donated one million yuan to the film, and the rest of money was raised through a crowd-funding program.
Zhang said she did not expect any return from her investment and was impressed by the powerful "strength of society" revealed by the film's box office performance.
She said the film was a "touchstone" that aroused many people's conscience.
Guo said he is pleased the documentary has received so much public attention, expressing hope that the younger generation will have a greater understanding of the history and experiences of the comfort women.
According to Taopiaopiao, a popular movie ticket-selling website under Alibaba Group, about 19.1 percent of the film's audience were people under the age of 19.
The most significant impact of the documentary is its ability to remind younger generation of what has happened in this country, said cultural critics "AD1874."
"[Their stories] had never been shown in such a true way," user "Nihao-Shanzha" posted on microblogging site Weibo. "This is history. This is part of the past that should never be forgotten."
"I felt uneasy for a long time after I walked out of the cinema ... I was feeling sorrow. These elderly women are leaving so fast but we are coming too late," said Li Jingfen, a teenage viewer.
"I have never seen a movie where the theater was quiet like this. The audience all left in silence after the film had finally ended, which included a long credit list of the names of the more than 32,000 crowd-funding donators," user "Juzimomo" wrote in a Weibo post.
