Transcript for Jessica Alba: 'Sin City' Character 'Opposite of Who I Am'
You know, for someone with such a celebrated figure, Jessica alba says she's a bit prudish about flaunting it. That is, unless she's in character as one of the sexiest, fearless good girls gone bad. I sat down with her co-stars, as they launch the wildly anticipated sequel to "Sin city." They're hoping to reinvent the comic movie genre. But did they succeed? Jessica alba knows how to work the curves of her physique. I have to ask the questions that e.q+ery mom is thinking. You had two kids and those abs? What the heck, man? Jennifer Johnson. She's choreographer. So much of it was getting comfortable dancing. I'm not a dancer. Getting comfortable on stage. And being able to go there and really kind of own it. Reporter: And the frequent cover girl doesn't disappoint. Playing an exotic dancer in "Sin city: A dame to kill for." I know exactly where I am. I know exactly what I am. Reporter: Jessica's character, Nancy, is starred by the loss of her love, Hartigan, Bruce Willis. So devoted to her man. And then, to have herrt hea broken and to be crushed and sort of like spoiled. Reporter: That's when it turns gritty. Horrifyingly edgy. It's Jessica alba like you've never seen her before. The movie is chock full of metaphor. What does it mean that she cuts her hair, cuts herself? Yeah, it's rad. Crazy's sounding pretty good right now. She's shedding people's perception of that sweetness. Reporter: Going from grieving lover to vengeful killer is going against type for this wholesome mother of two. You described yourself in some articles as a prude. That playing a stripper and being overtly sexual is not really your scene. No. Reporter: And yet, you push the envelope for this particular character. Yeah. It's fun. That's why it was so fun. It's the opposite of who I am. I run a company and have kids. Reporter: That company is the honest company, which makes nontoxic, eco-friendly baby products. And Jessica is at the helm, as CEO. Her reality is a far cry from the fantasy world she inhabits on the revved-up take on film noir. It's real. I can watch it. I normally have a hard time watching me. But I don't feel like there's any of me up there. It's Nancy. Reporter: It's not just Nancy. "Sin city," opening tomorrow, is bursting with epic and raunchy characters, straight out of the graphic novel. Shall we? Reporter: And yet these cartoons-come-to-life are played by Hollywood heavyweights. Even a cameo from the nearly unrecognizable, lady gaga. This won't take you very far. Sweetheart, it's going to take me to the moon. Reporter: The characters are also into seedy sex and stomach-churning violence. This violence is palpable and fun to watch because it's not realistic. Reporter: Even though you're being tortured? It's got a knowing humor to it. Reporter: Gordon Levitt plays a charmed gambler. But greed and arrogance lead him to beat the wrong guy at poker. This boy is good. Reporter: Then, there's josh brolin's tortured character, whose love for his ex, is leading him to depression. It's like a perfect metaphor for addiction. He sees her and that's all he needs. And he gets sucked right in. Right there is a dame to kill for. Reporter: And so does the viewer, who is sucked in by filmmaker Robert Rodriguez. Perhaps best known for his cult hits like "Dusk till dawn." And "Spy kids." Really starting to tick me off. Reporter: Rodriguez doesn't just direct, he shoots, edits, even composes the movie's music. And he uses the newest green screen to create this fantasy netherworld, like diving into a cartoon. I call it the dream screen. It's anything you want it to be. And you can move so fast and keep an actor in a flow because you don't have to change locations. You're going into this sort of magical dreamscape of a world. It's like being a kid and playing pretend. And I love that. Reporter: And yet, the explicit sexuality is far from child's play. In fact, it's a former bond girl from "Casino royal," that steals the show. She's kind of a psychopath. Do me one last favor, lover. Stay still long enough for me to blow your brains out. Reporter: What was it like to play a wicked Creech center. Ava is pure evil. And it's fun to play somebody that is free and irreverent. Sometimes I'm really shy. Reporter: She may be shy, but not about appearing naked in the film, multiple times. Was that hard at all? Of course. I don't know one actor that enjoys a nudity scene. You want to die. But for ava, nudity is a weapon, to get what she wants and become numb. You just do it. You forget in some weird way that you are naked. Reporter: Ironically, though she's not naked on the movie's poster, it sparked controversy, when the motion picture association of America banned it. On the poster, it's really suggestive. But you don't really see anything. And I find it sexy in a very tasteful way. Reporter: Eva's co-star came to her defense. We love in a prude country. They would rather send kids to war than show a woman's breast, which is something that's beautiful. This speaks to our ridiculous regulations in this country and priorities, frankly. Reporter: How old will your children have to be before they're allowed to see this movie? I think between 16 and 18. Reporter: And yet, they never saw "Spy kids" until your parents let them see it. I know. My parents. Reporter: But young kids are really not the target audience for this movie. Thousands of fan of the cult hit stood in line for hours at this year's comic-con, after nearly a decade of anticipation for this sequel. Fans all clamoring to descend into the decadent darkness of "Sin city." You have to show the dark side to show that redemption, proving that you're worth a damn. You have to go down deep and dark and descend, in order to come up.
This transcript has been automatically generated and may not be 100% accurate.