Mateo is an 18-year-old Puerto Rican teenager who lives a sheltered, isolated life indoors. He spends his time playing video games and reading online forums, paralyzed by his fear of the outside world. When Death-Cast informs him he has less than twenty-four hours to live, he uses an app called Last Friend to find companionship and forces himself to experience the city.

Rufus is a 17-year-old Cuban-American teenager who lives in a foster home affectionately called Pluto. He carries heavy survivor's guilt following a tragic accident that took the lives of his parents and sister. He is bold, outwardly tough, and intensely protective of his found family.

Aimee is a teenager who previously lived at the Pluto foster home before moving in with her aunt. She maintains strong feelings for Rufus despite their breakup and her new relationship. Her presence in Rufus's life creates tension, especially as the clock ticks down on his End Day.

Peck is a young man with ties to a local street gang. He recently started dating Aimee and intentionally provokes Rufus by badmouthing their past relationship. Following a humiliating physical defeat, he spends the day hunting Rufus down for revenge.

Malcolm is a tall, physically imposing foster youth who lives at Pluto. He entered the system after losing his parents in a house fire set by arsonists. He routinely sacrifices his own well-being to protect his friends.

Tagoe is a quiet foster youth at Pluto who wears glasses and manages a physical neck tic. He entered foster care after his mother abandoned him and his father committed suicide. He stays deeply loyal to the small group of boys who understand his history.

Lidia is Mateo's closest friend from high school and a single mother living in a small apartment. She dropped out of school to raise her daughter after her boyfriend died in a car accident. She relies heavily on Mateo for emotional support and friendship.

Delilah is a young editorial assistant working for Infinite Weekly magazine. She colors her hair to resemble the aurora borealis. When she gets her Death-Cast notification, she convinces herself it is a prank orchestrated by her ex-boyfriend and goes to work instead of saying goodbye to loved ones.

Victor works as a herald for Death-Cast, spending his shifts notifying people that they are going to die. He struggles with depression following a recent breakup. His job takes a heavy emotional toll on him.

Howie is a 25-year-old famous actor known for playing the villain in a popular science fiction movie franchise. Despite having millions of fans online, he feels entirely alone upon receiving his Death-Cast alert.

Deirdre is an employee at a business that provides safe, simulated extreme experiences for Deckers. She carries a history of depression and suicidal ideation stemming from childhood bullying.

Vin is a former wrestler who was forced to abandon his athletic career due to a genetic muscle disease. Bitter and furious about receiving his End Day alert, he decides to take out his anger on the gym where he used to train.

Zoe is an incoming college freshman at NYU who receives her Death-Cast alert before her first day of classes. Knowing no one in the city, she turns to the Last Friend app to avoid spending her final hours alone.

Gabriella is a graffiti artist who uses her skills to promote the Last Friend app around the city. She volunteers her time to accompany Deckers so they do not have to face death in isolation.

Officer Andrade is a police officer who responds to the disturbance call at the foster home. He relies on his instincts to determine which dying citizens pose an actual threat to the public.

Dalma is the creator of the Last Friend app, software designed to connect lonely Deckers with companions. She encounters Mateo and Rufus briefly while contemplating the impact of her work.

Damien is a self-described adrenaline junkie who previously ran a street gang. He readily agrees to reunite his old crew to help Peck violently confront Rufus.

Kendrick is a gang member who turned to violence after being bullied and robbed as a child. A stranger once showed him kindness after a beating, but he chose a path of aggression to ensure he would never be a victim again.

Andrea is the Death-Cast herald who calls Mateo to inform him of his impending death. She relies on emotional detachment to excel at her difficult job, viewing her notifications as a final chance for people to truly live.