Serena Frome is the protagonist and the narrator of Sweet Tooth, though the final chapter reveals that Thomas Haley is telling her story. This final reveal is telling of Serena’s character as a whole: she prefers to be the passive observer rather than the active instigator. She is a keen reader but does not ever entertain ideas of being a writer herself. Even in her career, Serena is happy to watch and take notes from afar rather than actively engage, making her an ideal candidate for the world of intelligence. Even her own life’s story is told by another person, though he does so with her permission.

Another of Serena’s defining traits is the need for love and validation. After growing up in a household with an emotionally distant father, she craves the attention of older or authoritative men. Men like Tony, Max, and Haley provide Serena with the validation she never received during her childhood. They are more mature, smarter, or in positions of greater power than Serena, meaning that she feels a need to please them as she feels a need to please her father. Criticism from these authority figures makes Serena feel small, transporting her back to her childhood.