Chinese President Xi Jinping is expected to attend the first national memorial day for the Nanjing Massacre on Saturday, as China marks a deeply symbolic anniversary while it tries to improve ties with old foe Japan.
China consistently reminds its people of the 1937 massacre in which it says Japanese troops killed 300,000 people in its then capital.
A postwar Allied tribunal put the death toll at 142,000, but some conservative Japanese politicians and scholars deny a massacre took place.
China and Japan have long sparred over their history. In March, Japan lodged a protest with China over comments in Germany by Chinese President Xi Jinping about the massacre.
Relations had deteriorated sharply over the past year following Japanese Prime Minister Shinzo Abe's visit to the Yasukuni Shrine honouring war criminals among Japan's war dead. The neighbours are also locked in dispute over islets in the East China Sea.
But both countries, mindful of the economic stakes, reached agreement last month to try to reset ties.
Xi, who met Abe in Beijing in November, is expected to attend the memorial in Nanjing, diplomatic sources told Reuters. He will have to tread a fine line between reminding Japan of what happened and not derailing the thaw in ties.
"They don't want to work things up," said a Beijing-based diplomat. "China wants to appear conciliatory while also not forgetting the past."
Tang Jiaxuan, a former Chinese foreign minister who heads a committee on improving relations with Japan, dispensed with the usual fiery words last week when talking about next year's 70th anniversary of the end of the World War Two.
"The 70th anniversary is an important opportunity for Japan to renew how it looks on and thinks of history, to unload its burden by facing up to and reflecting on history, to have real reconciliation with its Asian neighbours," Tang said.
That is not to suggest China will start playing down the massacre. In the days running up to the memorial, the government has been releasing accounts of the violence from its archives.
The Xinhua news agency carried excerpts from the diary of Nanjing teacher Cheng Ruifang, who recorded how Japanese soldiers "killed and raped at will, regardless of the victims' ages".
Still, one Shanghai-based Japanese diplomat said relations did appear to be improving following the Xi-Abe meeting, with China sending more senior officials to events in China sponsored by Japan.
"This is a reflection of the summit," he said. But he added a further improvement in ties "will be a slow grind".