As most of you probably know, Kick-Ass began shooting before Mark Millar's comic book mini-series ever came close to being completed. So the fact that director Matthew Vaughn and Millar have already begun promising a sequel before the second mini has even begun to be written shouldn't come as any surprise. Millar confirms that he will begin writing the second series in April, with hopes of a September completion to coincide with a possible DVD release of the film....
“I’m going to start writing in April and Johnny [Romita, artist] will hopefully have it out by September, to cash in on that DVD,” Millar says, probably half joking. “We’ll definitely see more of Hit Girl. I think we’ve stumbled onto the new Han Solo, there’s just something about this character that, from the minute she appears, we just went insane for her. We just loved her.”
Kick-Ass's conclusion pretty much spells out where any potential sequel might lead, but Millar makes no bones about the film's direction. Here comes the big spoiler....
“Red Mist becomes the Joker to [Kick-Ass], you know? But we’re talking about another villain as well,” Millar says, “so he’ll almost be a sidekick to this other guy. My working [name is] somewhere between the motherfucker and the cunts. That’s the two names I’m thinking of. I mean, it’s better than the Joker, isn’t it?"
Millar went on to indicate that the name of the second series could be Balls to the Wall, making up the 2nd part of a proposed trilogy, according to CHUD. Whether or not the film adaptations will also be a trilogy has yet to be determined, but assuming they are a success at the box office I'd say it's a lock. The main villain of the next story could be named either The Motherfucker or...The Cunts. Seriously.
Film School Rejects, I09, and Cinematical have even more coverage of Kick-Ass and this story in particular on their sites.