A 15-year-old living in Bluffton, Wisconsin, who suddenly experiences a massive growth spurt. He struggles with severe anxiety and trauma stemming from finding his father's body at age five. Mocked at school as "Squirrel Nuts," he isolates himself in his basement bedroom until his new size attracts the attention of the high school football team. He attempts to manage his physical changes while dealing with his mother's worsening emotional distance.

Felton's 13-year-old brother and a gifted piano prodigy. He prefers classical music and wears plastic glasses, presenting a vastly different physical image than his older sibling. He pays close attention to their mother's emotional state and feels fiercely protective of her. This loyalty often leads to intense clashes with Felton over household attitudes.

The single mother of Felton and Andrew who works as a crossing guard. She maintains a bohemian lifestyle, wearing sandals and practicing deep breathing exercises to manage stress. Following her husband's suicide, she burned all family mementos in an attempt to move forward. Recently, she exhibits increasingly detached behavior, retreating to her bedroom and crying silently.

A 16-year-old Black piano virtuoso from Chicago spending the summer in Bluffton. She and her father rent out Gus Alfonso's house. She plays the piano with intense passion and immediately catches Felton's eye when he takes over his friend's morning paper route. She possesses a confident, direct manner that contrasts sharply with Felton's nervousness.

The high school track and football star, and the son of the football coach. A few years older than Felton, he has a long history of bullying him. He feels threatened by Felton's sudden growth and exceptional speed, using his social status to publicly ridicule Felton during summer workouts.

A high school football player who notices Felton's physical growth. He actively recruits Felton for summer weight training and the football team. Having experienced bullying himself, he offers Felton encouragement and advice on how to carry himself with confidence in social situations.

Jerri's estranged mother who lives in Arizona. She maintains very little contact with her daughter and grandsons, sending occasional holiday cards but never visiting. Felton and Andrew grow up believing she actively dislikes them due to the family's strict physical and emotional boundaries.

Felton's best friend since childhood. Known for his long black hair and sarcastic sense of humor, he shares Felton's disdain for their small town. He leaves Bluffton to spend the summer in Venezuela visiting his dying grandmother, forcing Felton to take over his morning paper route.

Felton and Andrew's late father. He died by suicide in the family garage when Felton was five years old. Jerri describes him to the boys as a gentle, poetry-loving, unathletic man. His absence leaves a profound emotional void in the household, heavily contributing to Felton's lasting anxiety.

Aleah's father and a poetry professor from Chicago. He rents a house in Bluffton for the summer while teaching at the local college. He maintains a warm, communicative relationship with his daughter and treats Felton with polite, measured curiosity.

Felton's other childhood friend, grouping with Felton and Gus as the sons of local college professors. He rarely laughs at Felton's jokes and actively distances himself from Felton at the start of the summer, lying to avoid spending time with him.

A loud, crude member of the high school football team. Felton initially views him with intense dislike based on years of social division, but they begin interacting directly when Felton joins the summer weightlifting sessions.

A high school football player who heavily follows the team's established social hierarchy. He initially joins Ken Johnson in mocking Felton before Felton proves his athletic potential in the weight room.

A local girl who declared herself Felton's girlfriend in fifth grade before transitioning into actively bullying him. She is part of the popular sports crowd that Felton suddenly finds himself associating with over the summer.

A local girl who runs in the same popular athletic circles as Abby Sauter and the high school football team. She begins interacting with Felton once he gains social status through his new physical prowess.

The head coach of the high school football team and Ken's father. He recognizes Felton's raw physical potential and actively encourages him to join the team, viewing Felton's speed as a massive strategic advantage.