This is just an excerpt of the article in LATimes. Click on the site for the full article. Warning for Serious *SPOILERS*!
During production, the real Joan Jett was a semi-constant presence on-set. At the Kyoto Grand location, the rock icon huddled with Stewart conspiratorially in between takes, their closeness highlighting a remarkable physical similarity. In the film, Stewart convincingly channels something of Jett's androgynous, take-no-guff demeanor and rock star swagger. (Stewart declined comment for this story.)
"She has completely embodied the character of Joan," Sigismondi said. "Her body language, her face, her walk. It's amazing how she has just become her."
Production designer Eugenio Caballero was even more blunt. "Kristen is Joan," he said in between scenes. "You talk with her and you think it's Joan Jett."
The notoriously private rocker, whose post-Runaways project Joan Jett and the Blackhearts' "I Love Rock 'N Roll" famously hit No. 1 and has sold more than 10 million copies, did not want to be interviewed. But she admitted feeling a strange satisfaction while watching the actresses perform the Runaways' music.
"It's surreal, that's all I can say," Jett said. "But I have a smile on my face."
I just read the script for The Runaways (which I totally forgot I had) and the more I am excited for this movie. Kristen is so un-Bella in this one but I like it. We will all be blown away with Kristen as Joan Jett, and that is a promise.