"Reaper" is the latest track to drop off Sia's upcoming album This Is Acting, and like all the other songs on the album it was written for someone else. This thumping anthem was penned for Rihanna with some help from Kanye West, who also handled production on it. The triumphant song, about conquering your demons, wasn't originally supposed to be on the album, until someone close to Sia stepped in. ""It's a good, fun song, but I didn't anticipate it being on the record," she told Rolling Stone. "But my manager really likes it so I put it on for him." We all owe Sia's manager a high five, because this is a hit.