Mia’s best friend with freckles and red hair, who is processing her mother's death while dealing with her father’s new relationship and other teenage challenges.

Mia's older sister who has recently returned from a college prep program, embracing new interests that create some common ground with Mia.

Mia’s superstitious younger brother, known for his detailed record of McDonald's hamburgers, providing a contrast to their sister's vegetarianism.

Supportive but initially confused about Mia's synesthesia, they eventually help her learn more about it despite struggling to fully comprehend her experience.

A diligent student in Mia’s grade and her history project partner, who displays empathy and a level of maturity that contrasts with Mia's chaotic approach.

A 14-year-old boy with synesthesia whom Mia meets through an online forum, becoming her primary love interest and introducing different facets of teenage relationships.

A five-year-old boy with synesthesia whom Mia meets in the supermarket, whose story parallels Mia's as she tries to help him understand and accept his condition.

A neurologist at the University of Chicago who provides Mia with her synesthesia diagnosis and opens up opportunities for her to explore her condition further.