This birthday song was written for Smith's friend, the actor Johnny Depp. She explained during the playback for the album: "I went to visit him in Puerto Rico when he was filming Run Diary. It was his birthday and I didn't have a present, so I wrote him a song."
Smith told The Sun in 2012 about her friendship with Depp. "I met Johnny about five years ago," she said. "He and Vanessa (Paradis, his wife) and their daughter came to my concert in Los Angeles and said hello backstage. We just really hit it off. I lost my brother and really mourned him and it felt like he sent Johnny Depp to be my new brother. We love the same books. We talk endlessly about French literature and Jack Kerouac and Dylan Thomas. We just have fun and a laugh and he's such a great musician."
Depp also contributed some guitar to the title track of Banga.
Long-time associate Tom Verlaine of Television plays the guitar break on this track. "What Tom does in that guitar break on 'Nine' is unbelievable," Smith told The Sun. It's just like all the great records of the Sixties in just one run."