For years, China literally kept the tragic story of its "comfort women" underground.

Since 2007, the country's only museum dedicated to the women forced to work in Imperial Japanese Army brothels has overflowed two cramped rooms in a musty basement on the campus of Shanghai Normal University.

"The government said it's better not to do this research. Publishing was impossible. Why? For the sake of good relations with Japan," said curator Su Zhiliang, a history professor who has spent over 20 years painstakingly documenting the women's suffering.