ZJ is a pre-teen boy living in Maplewood, New Jersey, in 1999. While his father is a famous professional football player, ZJ prefers playing his guitar and writing songs over sports. He spends his free time riding bikes and eating grilled cheese sandwiches with his three closest friends, who call themselves the Fantastic Four. As his father's health begins to change, ZJ leans heavily on his music and his friendships for stability.

Zachariah is a famous tight end for a professional football team and a beloved figure in his community. He shares a strong bond with his son, regularly taking him for drives and writing rap songs together on weekends. After sustaining numerous concussions during his career, he begins experiencing severe headaches, memory loss, and sudden anger. He tries to pass his memories and love of music down to ZJ as his condition worsens.

Lisa is ZJ's mother and Zachariah's wife. She manages the household and takes the lead in seeking medical help when her husband begins displaying worrying cognitive symptoms. Frustrated by doctors who dismiss the connection between her husband's football career and his illness, she speaks privately with other football wives about similar problems. She works continuously to maintain a safe and stable home environment for ZJ.

Darry is one of ZJ's classmates and a member of the tightly knit Fantastic Four friend group. He loves music and is known for moving smoothly, frequently compared to flowing water. He relies heavily on his close friends for emotional support when his parents announce their separation, retreating to the trail with them for comfort.

Daniel is a sensitive and perceptive member of the Fantastic Four. He is an expert bicycle rider who performs dizzying tricks on a bike he calls a Magic Broom. Among the friends, Daniel is often the first to ask how the others are feeling and he genuinely listens to their answers, recognizing the seriousness of Zachariah Sr.'s early outbursts before the others do.

Ollie is ZJ's oldest friend and the fourth member of their group. Originally an orphan before being adopted by his mother Bernadette, he views Zachariah Sr. as an important father figure. He has a talent for math and can divide fractions in his head without bragging about his intelligence. He often comforts his friends by making them grilled cheese sandwiches.

Everett is an eighth-grade student who is repeating the grade and is noticeably larger than ZJ and his friends. He idolizes professional football players and dreams of going pro himself. While playing touch football, he routinely breaks the rules by tackling smaller kids, arguing that it makes the game more fun.

Bernadette is Ollie's adoptive mother and a close friend to Lisa Johnson. She frequently visits the Johnson household to talk in the kitchen, offering a safe space for Lisa to discuss the cognitive symptoms affecting multiple retired football players in their community.

ZJ's grandmothers both live in Arizona and maintain homes filled with photographic records of the family's past. They travel to New Jersey to help Lisa and ZJ when Zachariah Sr.'s condition requires significant family intervention.

Aunt Nan is an extended relative of the Johnson family. She travels to Maplewood to provide practical assistance and emotional support to the household when Zachariah Sr.'s health begins to require extra caretakers.

Uncle Sightman is a close family friend whom ZJ refers to as an uncle. He steps in to watch over ZJ during a medical emergency, ensuring the boy is not left alone when Lisa needs to attend to her husband's urgent needs.

Uncle Willy Daily is an old friend of Zachariah Sr. As Zachariah's memory begins to fail, ZJ helps his father recall Willy's name while they discuss stories from the football player's younger years.