Evidence has also shown that the victims of Japanese "comfort women" system spread across Asia and beyond, involving people from China, the Korean Peninsula, the Philippines, Malaysia and Indonesia, as well as the Netherlands and Russia. In Shanghai alone, the research team confirmed at least 182 "comfort stations", the highest number in the world, according to Su.

"The lack of documented records has made fieldwork extremely important in researching the 'comfort women' system, especially in China. As the original and primary implementation location of the system, China has the most eyewitness accounts and material evidence. It is an unavoidable responsibility for Chinese scholars to carry out this research," says Chen.

Dedicated to researching the system for over 30 years, the couple has been joined by many other domestic and international researchers, scholars and volunteers, including those from Japan. However, Su also warns about today's increasing "dangerous signal" of Japan's stance on these historical truths.

Back in the 1990s, Japanese school textbooks still included references to the "comfort women" system, which is becoming increasingly rare. Japan's current attitude toward this part of history is even more regressive than it was 30 years ago, says Su.