Astrid is the protagonist of the story and the character that experiences the most significant inner and outer transformations. Astrid also narrates the story in the first person, sometimes breaking the fourth wall by addressing the audience directly. She is a 12-year-old girl with dark, messy hair and baggy clothes. Astrid begins her summer as an emotional and sensitive girl who is unsure about doing anything without her best friend Nicole by her side. Astrid can also be cynical and often complains about being dragged to various events by her mother. One such event is a roller derby, and seeing the women’s fierce attitude, especially one named Rainbow Bite, inspires Astrid to learn the sport. Unfortunately, Nicole does not share the same interest in roller derby. Thus begins a period in Astrid’s life in when she is forced to grow and mature, as well as learn to be more empathetic and funnel her rage into a productive activity like roller derby.

Astrid begins showing a new, braver side of herself when she goes to roller derby without Nicole. All the girls look much older and seem very skilled, but Astrid barely knows how to skate.