Fern's twin sister, a self-described perfectionist struggling with her marriage and inability to have a child, whose complex relationship with Fern is central to the narrative.

Fern’s supportive boyfriend and a tech entrepreneur with similar sensory processing issues as Fern, who encourages her to reassess her reliance on Rose.

The mother of Fern and Rose, who is in a care facility due to brain damage, with a history that shapes the twins' childhood experiences and their perceptions of her.

Fern's supportive colleagues who help create a nurturing and stable environment for her at the library, offering protection and encouragement.