Mia's twin brother, optimistic and caring, who works at a therapy center for neurodiverse individuals and is passionate about special education.

Mia and John's 14-year-old brother with autism and mosaic Angelman syndrome, who is nonverbal but begins to communicate through alternative means.

Mia's mother, a PhD in applied linguistics, who is affectionate toward Eugene and struggles with guilt related to their communication challenges.

Father of the Parkson siblings, who is characterized by his philosophical interests and deep involvement in his children’s lives, despite being absent from the narrative after his disappearance.

A law enforcement figure involved in the search for Adam and issues surrounding Eugene, noted for her distinctive appearance and ambiguous intentions.

A lawyer for families at Eugene’s therapy center, depicted as competent despite her initially underestimated demeanor.

Eugene’s therapist known for her expertise with nonverbal clients, who insists on Eugene's intelligence and challenges existing perceptions.

Mia's ex-boyfriend, who demonstrates thoughtfulness and support for the Parkson family during Adam’s disappearance, and who has experienced systemic racism.