The Don't Be Afraid Of The Dark star will play Calista, the young ward of Christian Walker (Jason Patric), in the comic book adaptation.
"When you first see her in the beginning of the show, there's already kind of a thought, like there's something different about her," Madison told Spinoff Online. "She has a secret... and we don't reveal it in the pilot."
The actress also hinted that her character will evolve if Powers continues beyond the pilot episode.
"If the show does get picked up, there are some really fun things that my character is able to do," she said. "She's such a sweet girl, but in the same way she'll kick some butt if she needs to."
Madison also insisted that the pilot feels "so true" to the original comic series by Brian Michael Bendis,
"It's like you're watching a comic book," she claimed. "Everybody looks the same [as they do on the page]. I had pitch-black bangs [and] I was wearing a wardrobe that you'd imagine her to have.
"All the detailed sound and special effects are so realistic that I think when you see it, you're just going to want to hit pause so you can look at all the details."
Jason Patric and Lucy Punch will play the lead roles of Walker and Pilgrim. Charles S. Dutton will appear as police department head Captain Cross in the pilot, with child actress Madison playing Walker's young ward Calista.
Canadian model and actress Carly Foulkes is believed to have been cast as celebrity superheroine Retro Girl, and Supernatural's Alona Tal will also appear in an unspecified role.
> Powers pilot is Dark Knight meets Se7en, says exec