The director had wanted to use Jackie Chan's office as the set for C.N.'s apartment, but this proved impractical, particularly as that section of the office is on the third floor. However, many props from Chan's office were used, including his own training dummy. Chan said of his character, C.N., that he was "60-70% Jackie Chan." The clothing the character wears, the training routine he undergoes and healthy lifestyle he maintains, and his general good nature and his environmental role are all traits and actions of Chan himself.
The film was originally conceived purely as a love story, with Chan as producer, but not as one of the film's cast. In order to secure the actress Shu Qi, the script of the film was re-written and a role for Chan was created. This soon developed into a starring role, and elements of action crept in.