Kit is a high school student experiencing intense grief after the recent death of her father in a car crash. Formerly outgoing and popular, she feels entirely disconnected from her usual social circle and seeks out quiet, undemanding spaces. She suffers from severe insomnia and obsesses over the physical variables of her father's accident.

David is a highly intelligent, neurodivergent high school student who values honesty, routine, and prime numbers. Socially isolated and frequently targeted by bullies, he spends his time studying Krav Maga, researching quantum mechanics, and cataloging his peers' behavior in a notebook. He finds his solitary routine happily disrupted when Kit enters his life.

Lauren is David's popular and fiercely protective older sister, whom he affectionately calls Miney. Currently a college student, she unexpectedly returns home for an extended stay while privately struggling with her own academic and social adjustments. She acts as David's primary interpreter of high school social rules, offering blunt advice on peer interactions.

Mandip is Kit's mother, who works to maintain an outward appearance of capability and stoicism following her husband's sudden death. As the American-born daughter of Indian immigrants, she focuses heavily on practical matters and her career. Her reluctance to discuss emotional pain inadvertently creates distance between her and her grieving daughter.

Robert is Kit's recently deceased father, who worked as a dentist in Mapleview. Having lost both his parents to cancer at a young age, he lived cautiously and practically before dying in a sudden car crash. His passing leaves his family reeling and searching for answers.

Annie is one of Kit's closest friends at Mapleview High School. Bold and outgoing, she pushes her peers to be socially active and ambitious. She becomes frustrated by Kit's sudden need for distance and quiet, misinterpreting it as personal rejection.

Violet is Kit's other best friend, known for her preppy style and her role as the peacemaker in their friend group. Like Annie, she finds it difficult to support Kit through her grief and tries to encourage a return to their normal high school routines and parties.

Jack is Robert Lowell's best friend and the executor of his will. He acts as a surrogate uncle to Kit, frequently checking in on the Lowell household and assisting Mandip with end-of-life financial logistics following the accident.

Justin is a student at Mapleview High School and the primary bully targeting David. He feigns friendliness to manipulate David, holding a history of cruel behavior that includes an aggressive physical assault in the middle school locker room.

Gabriel is Justin Cho's best friend and an active participant in the bullying campaigns against David. He is also Kit's ex-boyfriend, and he continues to act possessively and flirt with her despite her clear disinterest.

Amy is David and Lauren's mother. She is fiercely protective of her son, enthusiastically encouraging his nascent friendship with Kit while actively advocating for him against school administrators who fail to support neurodivergent students.

Mr. Drucker is David and Lauren's father, a dedicated medical researcher. David often compares himself to his father, identifying similar neurodivergent traits in him and taking comfort in his parents' successful marriage.

Trey is a college psychology student who acts as David's guitar instructor. Without David's explicit knowledge, he also serves as a social skills tutor, gently pushing David to participate more actively in school events and peer interactions.

José is the second-smartest student at Mapleview High School, ranking just behind David. He persistently recruits David for the school's Academic League and seeks to emulate David's fashion choices after observing his wardrobe update.

Willow is a popular girl at Mapleview High School who frequently socializes with Kit's former friend group. She participates heavily in the local gossip mill and remains superficially concerned with school dances and peer social standing.