It has been rumored for a while, but Robert Rodriguez has now confirmed via an interview at Sundance 2013 that Bruce Willis will return for Sin City: A Dame to Kill For.
Rodriguez also talked about the usage of 3D in the sequel. He stated
they are filming in 3D so the dimension and stylization created will
"blow people's mind."
If you don't remember Willis' character in Sin City, he played a police detective named John Hardigan who was assigned to investigate a serial killer rapist. He discovers the suspect is the son of the most powerful man in the city, Senator Roark. Hardigan is shot after his partner frames him while attempting to rescue 11-year old Nancy Callahan. Roark frames Hardigan for the rape of Nancy and he spends 8 years in prison. Nancy is the only person to keep in contact with him over the course of his sentence and he accepts whatever comes at him as long as she remains safe.
Sin City: A Dame to Kill For will be released on October 4, 2013. The film also stars Joseph Gordon-Levitt, Rosario Dawson, Juno Temple, Mickey Rourke, Jessica Alba, Jaime King, and Josh Brolin.