The film is loosely based on the discovery of a key piece of evidence from the Nanjing Massacre. In 1938, 15-year-old darkroom apprentice Luo Jin secretly compiled photos of the atrocities-taken by Japanese soldiers-into an album and hid it. The album was later discovered by Wu Xuan, another Chinese civilian, who preserved it for years before handing it over to postwar authorities.
The director intentionally casts actors from diverse regions (Southern, Northern, Nanjing natives, and outsiders) to reflect Nanjing's role as a cultural crossroads. He encourages dialect performances, inspired by his grandparents, who communicate perfectly despite never losing their distinct regional accents.
The film's depiction of Japanese soldiers looting Nanjing's city wall bricks reflects historical accounts of materials taken for Japan's Hakko ichiu Tower. The still-standing monument contains over 370 stones from occupied territories, including more than 200 from China, with research indicating some originated from Nanjing.
The postman Su Liuchang's employee number (1213) coincides with the date when the Nanjing Massacre began - December 13, 1937.
Daichi Harashima's mother is a Chinese. He started as a child actor and todate he has appeared in 10 feature films and are Chinese movies.
