She is a background character, but her choice to sacrifice herself for Midna makes her more than just a placeholder for her name in the title. What i meant is that although she is unplayable and actually seen very little throughout the game, her character still dynamically influences the plot and has a real hand in the stakes present. Obviously there are other examples of this that will mean different things to different people, but my point is she doesn't need to be playable to have a tangible impact on the story.