Justin is an 11-year-old boy struggling with severe grief and panic attacks following the recent death of his mother, Helen. He lives with his older sister, Victoria, who works multiple jobs to support them financially. To ground himself during moments of high anxiety, Justin clutches a puzzle piece from the last puzzle he worked on with his mother. He is empathetic and thoughtful, relying heavily on his core friend group for emotional support.

Nia is one of Justin's oldest and closest friends. She is highly intelligent, confident, and assertive, frequently sharing trivia by starting sentences with "Did you know?" She approaches frightening situations with logic and a preference for scientific facts. Her practical nature provides the group with a steadying influence when they face unexplainable events.

Lyric is a resourceful and fiercely protective member of Justin's friend group. He views his friends as his chosen family because of a difficult home life involving his father's incarceration. He plays the harmonica and does not hesitate to use physical force to defend his peers when danger arises.

Zee is a formerly gentle boy who recently returned home after a mysterious one-year disappearance. Traumatized by his experiences, he exhibits erratic behavior, including sleepwalking and sudden outbursts of aggression. He covers his bedroom walls with dark paintings of monsters and speaks in cryptic rhymes to warn his friends about an impending threat.

The Seeker is a sinister supernatural entity tied to the childhood game of hide-and-seek. It enforces strict, twisted rules and communicates entirely through rhymes and riddles. Operating from an alternate dimension called Nowhere, it preys on the fears of children who disrespect the rules of its game.

Duke is a boy who has been trapped in the dark alternate dimension of Nowhere for 80 years. Having survived for decades, he possesses vital knowledge regarding the Seeker and the rules of Nowhere. He is extremely cautious and skeptical that anyone can defeat the monster, having acquired numerous personal fears during his long captivity.

Mary is a young girl serving as a guide to the rules of Nowhere. Trapped for nine years without physically aging, she carries a deep grudge against her older brother for abandoning her. She is logical and pragmatic, though she remains terrified of specific phobias she encounters in the alternate dimension.

Carla is Quincy's twin sister. She projects a tough exterior and often bullies other children in the neighborhood. Her abrasive demeanor serves as a shield to mask a fiercely protective instinct toward her easily frightened brother.

Quincy is Carla's twin brother. He is timid, easily frightened by bugs, and relies on his sister's dominant personality for protection. When strange disappearances begin, Quincy becomes highly anxious and dependent on his peers for direction.

Shae is a neighborhood girl who dislikes sweating and is not close friends with Zee. Her uncharacteristic insistence on playing hide-and-seek sets a chain of terrifying events into motion for the friend group.

Hyde is a young ice cream truck driver with a distinctive rippled scar on his cheek. He distributes ice cream wrappers printed with hide-and-seek facts and harbors a haunted, secretive demeanor. He possesses firsthand experience with the supernatural forces hunting the children.

Victoria is Justin's 19-year-old sister. Following their mother's passing, she balances college coursework with two jobs to financially support her brother. She is practical and hardworking, gently encouraging Justin to process his grief and clean out their mother's room.

Helen is Justin and Victoria's late mother, who died from cancer a little over a year ago. Her passing left a deep emotional impact on Justin. In Nowhere, a grotesque, decaying manifestation of her appears to exploit Justin's deepest fears and grief.

Mrs. Murphy is Zee's mother. She appears stressed, exhausted, and bears unexplained scratches on her arms. She attempts to help her son readjust to normal life but finds herself overwhelmed by his severe sleepwalking and erratic outbursts.

Rodrigo was Zee's roommate at an art camp when Zee vanished. He holds vital clues about the supernatural circumstances of the disappearance, though he initially hid the full truth from the police out of fear.