On Thursday, Li Meijin, the last of the 22 elderly women that appeared in the documentary Twenty Two that recorded the Imperial Japanese Army's sexual slavery in China and other parts of Asia during World War II, passed away.

Li is one of the more than 200,000 Chinese women forced to be "comfort women", sexual slaves that suffered from repeated rape and abuses at the hands of the invading Japanese. She did not receive a deserved apology from the Japanese government even 78 years after the unconditional surrender of Japan. Nor did any of the other women.

The Japanese government has lost the opportunity of mending its broken conscience by issuing an official, formal apology to the victims. As long as there are still records of history, Japan will be known as a cowardly nation that dares not face up to its historical war crimes.

For China and other nations that suffered from Japan's militarist and expansionist ambitions, Li's death should sound an alarm about the urgency of preserving the collective memory of that part of history. Those who experienced it should be interviewed and audiovisual records of their testimonies should be preserved. With the elapsing of time, the number of firsthand witnesses to the atrocities committed by the Japanese forces is rapidly diminishing.

In 2012, when director Guo Ke made his first documentary about Japanese army's sexual slaves, it was titled Thirty Two because that was the number of known victims still alive.

In 2014, when Guo started a new documentary for a more detailed preservation of that part of history, it was named Twenty Two because that was the updated number.

In 2017, when Twenty Two was put on screen, only eight of the 22 interviewees were still alive.

Now the last of them has died. And they are only some of the victims of the Japanese occupation, among whom there are those who were tortured as medical guinea pigs, forced to labor in Japanese mines as slaves, or who lost their lives in massacres perpetrated by the Japanese army. More than 78 years after the end of World War II, only very few of them are still alive and can recount what they experienced.

It's time to act before it's too late.