Nina is a media editor living in New York who finds herself struggling with her need for control in a suddenly unpredictable world. As a media professional, she is acutely aware of how information shapes public perception and government policy. Her long string stands in contrast to her partner Maura's short one, forcing her to confront the limitations of her ability to protect the people she loves.

Maura is a queer Black woman in her late thirties who discovers she has a short string. Intelligent and fiercely principled, she recognizes the parallels between the emerging string-based discrimination and the racial prejudice she has experienced her whole life. She joins an evening support group at a local school to find a space where she can freely express her anger and vulnerability.

Amie is Nina's younger sister and a fifth-grade teacher in Manhattan. She is a romantic who views the world through the lens of the books she reads and teaches, heavily idealizing a specific apartment building called the Van Woolsey. Uniquely among her peers, she actively chooses not to look at her string, preserving her sense of mystery while living in an increasingly fractured society.

Ben is an architect whose life is upended when his girlfriend opens his box without permission, discovers his short string, and abruptly ends their relationship. Heartbroken but thoughtful, he attends a short-stringer support group to heal. He soon begins an anonymous correspondence with a stranger by leaving letters in a classroom, allowing him to safely explore the emotional implications of his shortened timeline.

Jack Hunter is a recent military academy graduate hailing from a wealthy family with a long history of military service dating back to the Revolutionary War. Despite his long string, he feels ambivalent about his predetermined career path and pressured by his family's imposing legacy. He shares a deep, brotherly bond with his roommate, Javier, which eventually tests his loyalty to his powerful relatives as new discriminatory laws threaten their futures.

Javier is a Latino military academy graduate with a genuine, profound commitment to serving his country. Coming from a close-knit family, he views his military career as a true calling rather than an obligation. When he receives a short string, he must figure out how to pursue his dreams and protect his parents from the painful truth of his timeline.

Anthony Rollins is a prominent politician and presidential hopeful who seizes upon the arrival of the boxes to boost his campaign. Convinced that his long string proves he is chosen by God, he shamelessly leverages fear and drafts discriminatory legislation against short-stringers to consolidate his power.

Katherine is Anthony's wife and Jack's aunt. Coming from a wealthy and privileged background, she views her long string as a sign of merit and cosmic justice. She fully supports her husband's political ambitions, utilizing her family's prestigious military legacy to bolster his campaign events.

Hank is a dedicated medical professional who resigns in frustration when his hospital refuses to treat short-stringers purely based on their string length. Holding a short string himself, he keeps his status a secret from his colleagues before eventually finding solace in the same support group attended by Ben and Maura.

Wes Johnson is a United States Senator running against Anthony Rollins for the presidency. When it is revealed that he possesses a short string, he becomes a prominent political figure pushing back against institutional discrimination and advocating for equal rights.

Claire is Ben's former girlfriend. Upon the arrival of the boxes, she looks inside Ben's box without his consent. Unable to face the reality of his short string, she immediately breaks up with him, leaving him isolated.

Lea is an expectant mother attending the short-stringer evening support group. She is acting as a surrogate for her brother and his husband, finding immense purpose in creating life despite her own shortened timeline.

Annika is a hospital colleague of Hank's with whom he shares a burgeoning relationship. She inadvertently discovers the secret of his short string, forcing Hank to reevaluate how he spends his remaining time.

Cal is Jack's deceased grandfather, a World War II veteran. His stories of military training and his personal philosophy on life and death deeply influence Jack's worldview as Jack prepares to graduate from the academy.