The documentary features interviews with the 26 veterans－aged between 88 and 95－whose military duties varied from scouting the enemies' positions to giving medical care to the injured.

Ren Hongju, a Beijing native who crossed Yalu River in 1951, serves to some extent as the "backbone" of the documentary with his talent for arresting storytelling, honed as a former member of a military art troupe, recalls Song.

Later promoted to the role of war reporter, who interviewed many soldiers in caves and trenches on the battlefields of the Korean Peninsula, Ren has "an exceptional memory for details", says the director.

As the first veteran to appear in the documentary, Ren is seen in the opening scene wearing dozens of medals over his military uniform, speaking softly to convey some of the most traumatic moments of the war.

Some of his memories recounted in the film include the gruesome death of a young troupe actress, who once played the lead in the well-known story of the White-Haired Girl, and the time the then 17-year-old Ren sneaked into a nearby village on a scouting mission and was horrified to discover a cohort of enemy soldiers asleep in one of the houses.

There are also some heartwarming scenes in the documentary, including one in which two female veterans have a joyful reunion after many years.

For Song and his crew, the project took them on a special journey to revisit history from a more private perspective, and redefine their idea of heroes.

"All those soldiers who survived the war and returned safely to China are heroes. Their stories deserve to be heard by more people and history should never be forgotten," says Song.