A 13-year-old eighth-grader whose life revolves around playing the drums in the All-City Jazz Band and managing his crush on a popular classmate. Known for his sarcastic sense of humor and self-deprecating nature, Steven struggles to process his emotions and responsibilities when his family faces a sudden medical crisis. He uses drumming and private journal entries to cope with his changing home life.

An accountant and the sole financial provider for the Alper family. He handles stress by withdrawing emotionally and throwing himself into his work. This avoidance strains his relationship with his teenage son during the family's medical crisis.

An English teacher who takes an immediate leave of absence to become the primary caretaker for her youngest son. She oversees doctors' appointments and frequent trips to the hospital in Philadelphia, carrying immense emotional weight while managing the household.

Steven's precocious, energetic, and talkative five-year-old brother who is diagnosed with leukemia. Despite his illness and the severe side effects of chemotherapy, he remains cheerful. He utterly idolizes his older brother and relies on Steven for comfort, often using his Matt Medic action figure to channel bravery.

A talented pianist and the only other eighth-grader in the All-City Jazz Band alongside Steven. She is exceptionally empathetic, highly observant, and frequently checks in on Steven's well-being, though he often misunderstands her intentions.

A popular cheerleader at Steven's school and the long-time object of his affection. She has a high school boyfriend and initially pays little attention to Steven, though they occasionally interact during school activities.

A teenage cancer patient who bonds with Steven over their shared age and her fascination with his everyday school experiences. Having undergone multiple treatments, she offers Steven a vital perspective on sibling support.

The middle school counselor who becomes an essential resource for Steven. She helps him manage his anxiety and academic struggles by advising him to focus on actionable steps rather than circumstances beyond his control.

Steven's observant English teacher. She cares deeply about her students' well-being, reading their journal entries to monitor their progress, and is one of the first educators to realize Steven is struggling with a secret.

The enthusiastic director of the All-City Jazz Band. He recognizes Steven's talent early on and mentors him, expecting high musical standards while actively supporting his students.

Steven's long-time private drum teacher. He enthusiastically supports Steven's musical ambitions and acts as a positive adult figure in his life outside of school.

A high school sophomore who plays guitar in the All-City Jazz Band and dates Renee Albert.