Through careful research, the doctors in Shanghai drafted an alternative, yet highly risky, plan. They decided to operate on her leg, get the infected bones out, remove the cancer cells and then reinstate the bones.

Unfortunately, the plan did not work because the cancer had metastasized and reached her lungs. Sirong chose to return to her hometown and spend her last days with her family. The documentary records the moment of her flashing a big smile as fireworks light up the night sky to mark the Spring Festival of 2018, which was her last Chinese Lunar New Year.

"I was in my 30s when I was making the documentary on her," says Fan, now the father of a toddler. "I remember the nights that I stayed in the office to edit the interview clips. It was difficult to hold back my tears."

Another protagonist of Once Upon a Life is Xu Lieying, a 35-year-old native of Fujian province whom Fan met at a Renji Hospital ward where critically ill pregnant women are treated.