Three years later, as efforts intensified nationwide to improve living conditions and protect the local ecosystem, the first batch of 2,900 residents from Tsonyi county was relocated nearly 1,000 km south to the north bank of the Yarlung Zangbo River, at an altitude of 3,600 meters, which is lower than Tsonyi's average altitude of around 5,000 meters.

When the relocation campaign drew to a close in 2021, Cai revisited the county for follow-up interviews. These encounters inspired him to codirect the 95-minute film Puruo Gangri with Zhao Hantang, known for the 2017 Xizang-set film Seventy-Seven Days.

More interviews followed, each adding moving moments to the project. One particularly striking interview took place in April 2023. Zhang Kunyuan, a government official who assisted Cai during fieldwork, showed him an old photo taken 11 years earlier when Zhang had just begun working in Tsonyi.

The young man in the picture had thick, black hair. Today, he is bald, with eyes red and swollen from years of living in harsh conditions. This dramatic change in appearance prompted the director to create a plotline for a major character in the film.