Content Warning: This section mentions miscarriage, the death of a parent, and a car accident.

Arianna is the main character of the novel. She is also one of the primary first-person narrators of Say You Swear. In the narrative present, Arianna is 18 years old. She lives in Southern California with her parents and twin brother, Mason. For as long as Arianna can remember, she and Mason have been attached. Although she knows that some people “might call that being codependent,” she “simply call[s] it a twin thing” (6). Arianna is glad that she and Mason are both attending Avix University after they finish high school. Their best friends, Brady, Chase, and Cameron, are also attending Avix. Because they have grown up together, Arianna sees her friends as an extension of her family. She relies on them for strength and support and is hopeful that they’ll remain close even as they get older.

Arianna is a sensitive, caring, and empathetic character. She values friendship and family above everything else and does everything in her power to ensure that her loved ones are happy and safe. When she and Chase have sex and Chase immediately pushes her away afterward, Arianna is heartbroken.