Jack is a high school senior who feels like he never quite succeeds at anything he tries. He forms a strong bond with Kate after meeting her at a college party at Whittier University. Self-deprecating humor masks his insecurities. He harbors a secret crush on his best friend Jillian, which places him in a state of emotional conflict as he attempts to navigate his social life.

Kate is a first-year college student who bonds with Jack over their shared appreciation for cereal and corny jokes. She lives with sickle cell anemia, a chronic condition she hesitates to share with others for fear of being treated differently. She matches Jack's witty banter and encourages him to take chances.

Franny is a tall, athletic high school student who has been Jack's best friend since childhood. He lives with his grandmother and deals with the emotional fallout of his father's incarceration. He plays in a band with Jack and Jillian. He demonstrates strong dedication to his close circle.

Jillian is the valedictorian of her high school class and completes the trio of best friends alongside Jack and Franny. She dates Franny but remains completely unaware of Jack's long-held crush on her. She values loyalty highly. She deals with financial stress at home after her father's abrupt departure.

Nina and Abe are Jack's highly supportive and loving parents. They prepare to celebrate their thirtieth wedding anniversary. They provide Jack with strong moral guidance and serve as models for what a healthy, committed romantic relationship looks like.

The Coupon is Franny's father, a man who has been incarcerated for eight years. He prepares for his release, which causes significant emotional distress for Franny. He struggles to reintegrate into society and repair the damaged relationship with his son.

Abuela is Franny's grandmother and primary caretaker during his father's incarceration. She works hard to support Franny and pushes him to be the bigger person regarding his father's mistakes.

Dr. Sowunmi is a medical specialist researching experimental treatments for sickle cell disease. His expensive protocols offer hope for patients like Kate, though financial barriers restrict access to his care.

Xander is Kate's ex-boyfriend who remains somewhat involved in her life. He knows about her medical condition and has supported her through health crises in the past, complicating Kate's readiness to move on.

Regina is Kate's mother. She stays by her daughter's bedside during medical emergencies and ultimately delivers tragic news to Jack during the first timeline.

Reggie is Kate's younger brother. He acts protective of his sister and gives Jack a playfully hard time when he comes over for a family meal.