Tomorrow I'll Be Nine by Eels is a reflective and emotive song that captures the bittersweet moment of growing up. The song is narrated from the perspective of a child on the eve of their ninth birthday, contemplating the passage of time and the inevitable changes that come with it. Key themes include innocence, coming of age, and the fleeting nature of childhood. Poignant moments in the song highlight the child's awareness of both the excitement of growing older and the nostalgia for the simplicity of earlier years.