Kick-Ass is the ultra-violent (surprise, it's Millar) story of a high school dork, Dave Lizewski, who reinvents himself as a superhero named Kick-Ass. Unfortunately, he's pretty bad at it, until he's forced to face real bad guys, who pack real weapons.
Surprisingly, Mintz-Plasse will not be playing the lead -- he's playing the Red Mist, the angry teenage spawn of a mob family, who tries to uncover the Kick-Ass' real life identity. Moretz will be playing a vicious, foul-mouthed 11-year-old who chops down criminals with a katana. (In other words, she's playing my future daughter. What can I say, I'm going to raise her right.) The lead has yet to be cast, and Vaughn is courting several big names to play parents and mobsters.
Now about Vaughn -- according to The Hollywood Reporter, he originally brought the project to Sony, who had served Layer Cake so well. They liked it, but wanted him to tone the violence down, which Vaughn refused to do. Several other studios were interested, but wanted him to make the violent protagonists older, which he also balked at. So now he's going the indie route, producing it with his Marv Films partner Kris Thykier. Despite the violence, I doubt he'll have trouble finding a distributor in the end -- the combo of Vaughn and Millar will have someone in Hollywood salivating.
If you're curious to read any of Kick-Ass, IGN has a preview of the first issue up. You gotta love the rapid succession of name drops on page five. I can't decide if it will be a lot of fun, or a really disturbing version of Spy Kids.