Michelle Yeoh had initial doubts about the role as she had not used her martial arts skills since Crouching Tiger, Hidden Dragon (2000).
The film's cast includes actors from Taiwan, Korea, Hong Kong and China. John Woo stated that "It is a challenge for all. We selected various talented actors for this film and the language seemed to be the main obstacle...But we solved that."
Ah-Sheng had an unusual accent because he was portrayed by a Korean actor. The Korean language is famous for not having accents or tonal variations.
After being impressed with the script, John Woo was reportedly on set the whole time offering advice to Chao-Bin Su. Terence Chang stated that Woo spent "more than a week" directing a fight scene featuring his daughter Angeles Woo as an assassin. Woo has stated that he "didn't want to impose my style on Su...I only gave advice and shared my experience."
The idea for making the film came about when producer Terence Chang was looking for an action film to star Michelle Yeoh. After several meetings with Chao-Bin Su they developed a wuxia style film.