For Kinohachi, who began to work as a professional shakuhachi player at the age of 19, the instrument has become part of his life.

"Shakuhachi has enabled me to maintain a living and has also brought me a lot of opportunities to communicate with people around the world," says Kinohachi.

"I was also thrilled to discover through the documentary that some youngsters in China such as Xu Haopeng have become self-taught shakuhachi players, thanks to the internet," he adds.

Born in the 1990s in Anyang, Henan province, Xu became fascinated with shakuhachi after hearing a few tunes online. Going against his father's wishes to study pharmacy and pursue a steady career, Xu saved up to purchase his first flute, and has now been studying the instrument for three years.

However, documentaries remain a rare niche in China's huge film market. Last year, only 18 films out of the 300-plus features making it to general release were documentaries, grossing 534 million yuan - just 8 percent of the total revenue earned by Chinese films in 2018.

When asked if she is concerned about the film's market performance, Yu says she just made the documentary out of love and passion. "I didn't think too much about the box-office returns. I just hoped that such a beautiful sound would be heard by more people".