The film was Robin William's new film 'August Rush' directed by Kirsten Sheridan. The film is about a boy on a magical music journey.
Ku's agency YG Entertainment said that “The film director personally extended an invitation and that Ku went to New York in March for the shoot."
The actress said, "I made a cameo appearance as one of the wandering artists Robin Williams looks after in the film. It was a tiny role but I was greatly inspired by the delicate workings of a Hollywood film set and the actors' freely expressed talent. My appearance wasn't important. I'm just grateful for the experience."