"I was stunned. I specialized in the social history of Shanghai, yet I had never heard of this," recalls Su, who immediately started collecting and studying documents about the system in Japan in 1992. He returned to Shanghai the next year to gather more information about the history and to search for survivors and witnesses.

Despite the astonishing number of victims, it has not been easy to find "comfort women" survivors, as many died during captivity or passed away over time. For potential living survivors, their stories had to be confirmed, which requires concrete proof of every incident, including a recorded first-person narration and material evidence. This meant forcing survivors or their kin to relive their traumatic past, Su says.