Claire's best friend, who shares her interest in science and is working to maintain friendships with both Claire and her new friend Emily. Casley is empathetic and emotionally mature.

Casley's new friend who initially seems to Claire like an antagonist due to her appearance and popularity. Despite facing personal challenges, she becomes a supportive friend to Claire and Casley.

Claire's older brother, who attends the same middle school and is initially presented as a source of conflict for Claire. He later supports her, proving to be a loyal and kind sibling.

Julia and David Koster, who both run their own businesses. David's ghost tours are a source of tension with Claire, while Julia provides support through her cooking and "teachable moments."

A classmate with whom Claire has a crush. He is characterized by his kind nature, and his connection to Emily is revealed later in the story, enhancing his role in the social dynamics.

A young ghost from a historical tragedy who appears to Claire. His haunting presence connects with Claire on a deeply personal level, and he is a key figure in the narrative's exploration of history and remembrance.