This song was written about Canadian serial killer Karla Homolka. Frontwoman Mish Way explained to NME:
"The song Sister is in the voice of Karla Homolka, a Canadian girl married to a man called Paul Bernado. They were known as the Ken and Barbie killers in the 1990s. They raped, murdered and tortured three girls together, one of them being Karla's little sister Tammy. So I imagined Karla apologizing to Tammy."
The video for Iggy Azalea's "Fancy" pays homage to the classic 1995 film Clueless with the rapper playing Cher and featured singer Charli XCX portraying Tai. It was filmed at some of the same locations used in the movie.