Autumn is an imaginative, somewhat quirky high school freshman who aspires to be a published author. She begins high school feeling isolated after drifting apart from her childhood best friend and the popular crowd. To establish her own identity, she begins wearing tiaras every day and forms a new clique that meets on a set of stairs called the "Steps to Nowhere." She experiences periods of clinical depression and relies heavily on her new social circle for emotional grounding.

Finny is the son of a single mother and the next-door neighbor to the Davis family. He spends his early childhood as Autumn's closest companion before they separate in middle school over social differences. In high school, he plays soccer, drives a red sports car gifted by his absentee father, and dates a girl named Sylvie. Despite running with the popular crowd, he remains highly observant and quietly protective of Autumn from a distance.

Jamie is an eager and forward high school student who quickly becomes Autumn's first serious boyfriend. He brings his cousin Brooke and his friend Noah into Autumn's social circle, helping to form their core clique. Jamie is highly focused on traditional milestones, frequently discussing marriage, careers, and intimacy while they are still young teenagers. He pushes Autumn to abandon her writing ambitions in favor of a practical teaching career.

Sasha is Autumn's closest friend during high school. The two bond over feeling excluded from the popular crowd and decide to form their own clique on the fringes of the school courtyard. Sasha focuses heavily on dating and social dynamics, frequently discussing boys, taking quizzes in magazines, and maintaining an on-again, off-again relationship with her boyfriend Alex.

Angelina is Finny's mother and a middle school art teacher. She raises her son single-handedly following a brief affair with a man who initially denied paternity. She is an independent, pragmatic woman who serves as a secondary maternal presence for Autumn, particularly stepping in when Autumn's own mother struggles with severe depression. She warmly supports Autumn's quirks, including buying her new tiaras.

Sylvie is Finny's girlfriend throughout high school. She belongs to the popular crowd that Autumn purposefully avoids. Sylvie maintains a tense distance from Autumn, driven by the unacknowledged history between Finny and his former best friend. Her friend group occasionally clashes with Autumn's, most notably in a turf war over a lunchroom table.

Autumn's mother is a woman who experiences periods of severe depression that occasionally require hospitalization. She leans heavily on her best friend, Angelina, for day-to-day support when her husband is away or her mental health declines. Despite her struggles, she tries to maintain family traditions like holiday dinners and firework viewings at the lake.

Autumn's father is a career-driven man who is frequently absent due to business trips. He is somewhat detached from his daughter's daily life, failing to notice her habit of wearing tiaras until months after she starts. His lack of presence and emotional distance creates significant tension in his marriage.

Brooke is Jamie's cousin and one of the core members of Autumn's high school friend group. She brings her boyfriend Noah into the circle. Brooke navigates the complex social and romantic pressures of high school alongside Autumn, occasionally struggling with fidelity in her own relationship.

Noah is Brooke's boyfriend and a steady presence in Autumn's social circle. He frequently hosts the friend group at his house for activities like building snow ramps for sledding. He is close friends with Jamie and generally easygoing.

Alex is Sasha's boyfriend. Their relationship is characterized by frequent breakups and reconciliations. He is part of the larger social circle but primarily interacts with the group through his connection to Sasha.

Angie is a member of Autumn's core friend group. She begins dating a boy named Dave, and the two rapidly reach major life milestones together while still in high school. Her experiences provide a contrast to Autumn's slower-paced relationship with Jamie.

Dave is Angie's boyfriend. He is vetted by the other boys in the group, including Jamie and Noah, who quickly decide he is a good match for Angie. He is supportive of Angie as they navigate serious life events together.

Jack is one of Finny's close friends. He occasionally bridges the gap between Finny's social world and Autumn's, inviting her to watch horror movies and hanging out with both of them. He is fiercely protective of Finny's emotions.

Dr. Singh is the psychiatrist Autumn visits when she begins struggling with the winter blues and deep sadness. He evaluates her and prescribes antidepressants to help manage her mood disorder.

Mr. Laughegan is an honors English teacher whose class is shared by Autumn, Jamie, Sasha, Finny, and Sylvie. Autumn quickly bonds with him over their mutual appreciation for literature, prompting mild jealousy from Jamie.