Sunny is a 13-year-old elite track star for the Defenders who dominates the mile event but feels unfulfilled by the sport. He carries profound guilt over his mother's death during his birth and faces a strained relationship with his father, who pressures him to run in her memory. Feeling suffocated by these expectations, Sunny secretly harbors a passion for dance and movement, using a diary to process his rapidly moving thoughts.

Darryl is Sunny's father, a natural planner who shut down emotionally after his wife's sudden death during childbirth. He pushes his son to excel in track as a way to honor his late wife's memory, though his intense scrutiny creates distance between them. He asks Sunny to call him by his first name because he feels he cannot be a true father without his wife to co-parent.

Aurelia is Sunny's artistic, eclectic homeschool teacher and his late mother's former best friend. She is recovering from addiction and celebrates 20 years of sobriety with annual green star tattoos. She acts as a vital link between Sunny and his mother, encouraging his interest in dance and providing unconditional support when he decides to quit running.

Coach is the stern but deeply supportive head coach of the Defenders track team. He views his athletes as whole people and prioritizes their well-being over winning. When Sunny admits he no longer wants to run, Coach creatively adapts by offering him the discus event and providing extra practice time.

Regina is Sunny's mother and Darryl's wife, who passed away from an amniotic embolism during Sunny's birth. She was a passionate dancer and a deeply caring friend who helped guide Aurelia toward sobriety. Though absent, her memory profoundly influences the lives, struggles, and decisions of her family.

Gramps is Sunny's grandfather who works at a local hospital. He acts as a supportive family figure, facilitating Sunny and Aurelia's visits to dance for the hospital patients. He occasionally mediates between Sunny and Darryl to encourage better communication.

Mr. Rufus is a hospital patient and former dancer who deeply appreciates Sunny and Aurelia's visits. He connects with the music and serves as an inspiration for Sunny's growing understanding of art and movement, even as his health rapidly declines.

Patina is a fellow runner on the Defenders track team. She is a loyal friend who quickly steps up to defend Sunny from teammates who criticize his decision to quit running the mile.

Lu is a member of the Defenders track team and one of Sunny's close friends. He supports Sunny's unexpected transition from running to throwing the discus, standing by him during difficult practices.

Ghost is a member of the Defenders track team who stands by Sunny as he explores his new athletic path. He shows up to cheer him on during his difficult transition away from running.

Mr. Nico is Sunny and Darryl's neighbor who founded the custom puzzle company Darryl invested in. He provides the family with the photographic puzzles of Sunny's mother and persistently encourages Darryl to start dating again.

Ms. Linda is Mr. Nico's sister. She represents a potential new chapter for Darryl as he tentatively begins dating again after years of mourning his wife's passing.

Lynn is a runner on the Defenders track team who questions why Sunny is still at practice and stretching if he is no longer competing in running events.

Aaron is a runner on the Defenders who antagonizes Sunny, telling him he shouldn't be talking because he is no longer a runner.

Fish is a large tattoo artist who regularly inks Aurelia's wrist. He knows her history and annually adds a green star tattoo to commemorate her years of sobriety.