Cassie is a determined, sarcastic sixteen-year-old girl surviving in the ruined state of Ohio after alien attacks wipe out most of humanity. Driven by a fierce love for her family, her primary motivation is a promise she made to find her younger brother, Sammy. Though hardened by trauma and constantly battling paranoia, she retains her core humanity and compassion.

Before the invasion, Ben was a popular high school football star whom Cassie admired. Now, he is a guilt-ridden survivor haunted by his failure to protect his family. Brought into a harsh military boot camp and rebranded with the nickname "Zombie," Ben pushes himself to become a ruthless soldier in hopes of avenging humanity and finding a sense of redemption.

Evan is a handsome young man living on an isolated farmhouse, where he claims to be the sole survivor of a large family. He takes Cassie in and nurses her back to health, providing her with food, shelter, and companionship. He is remarkably capable, observant, and deeply devoted to ensuring Cassie's survival.

Vosch is the commanding officer of the military forces at Wright-Patterson Air Force Base. He presents himself as a rigid, authoritative savior of humanity, organizing the survivors into combat units. He operates with ruthless efficiency and shows no hesitation in using violence to maintain control.

Sammy is Cassie's five-year-old brother, a sweet and observant child swept into the military machine at Wright-Patterson. Given the nickname "Nugget," he relies on his teddy bear and the memories of his sister to cope with the frightening reality of boot camp. His innocence grounds the older characters who fight to protect him.

Dr. Pam is a clinical, manipulative medical official who oversees the processing and psychological conditioning of new arrivals at the military base. She utilizes the Wonderland program to extract memories and test the loyalty of recruits like Ben and Sammy.

Ringer is an exceptionally talented sharpshooter and a pragmatist in Ben's squad. Fiercely independent and highly observant, she sets strict boundaries with her peers and actively questions the military leadership's official story, pushing Ben to think critically about their situation.

Reznik is the cruel, demanding drill instructor in charge of Zombie's squad. He uses humiliation and psychological pressure to break the child soldiers down, aiming to forge them into ruthless fighters for the military's cause.

Cassie's father is a practical, deeply loving man who struggles to keep his family alive through the alien waves. He reluctantly submits to military authority at Camp Ashpit in a desperate bid to give his children a better chance at survival.

Cassie's mother is a resilient woman who perishes during the third wave, an Ebola-like plague spread by birds. Her death shatters the family's sense of security and forces them to leave their home for a survivor camp.

Sissy is Ben Parish's younger sister. She is tragically ripped from Ben's arms during an attack on their home, and her loss becomes the central guilt that drives Ben's transformation into a soldier.

Ben's father is a protective parent who extracts a promise from Ben to watch over the family moments before being killed during a violent home invasion.

Ben's mother is present during the devastating attack on the Parish household, and is presumed dead alongside her husband and daughter.

Hutchfield is an ex-Marine who acts as the leader of the Camp Ashpit survivor community. He relies heavily on his firearm and incorrectly trusts the military forces that arrive to collect the children.

Crisco is a thirteen-year-old survivor orphaned by the early waves. He scavenges through the camp's ash pit for items to barter and harbors an unrequited crush on Cassie before meeting a tragic end.

Tank is a child soldier in Zombie's squad who suffers a mental breakdown from the immense pressure of their environment and is subsequently sent to the psychiatric ward.

Dumbo is a twelve-year-old recruit who serves as the designated medic for Zombie's squad, tasked with patching up his fellow child soldiers during their dangerous missions.

Flintstone is a seventeen-year-old recruit in Ben's unit. He is deeply indoctrinated by the military's rhetoric and strongly resists Ringer's rebellious theories.

Oompa is a member of the child soldier squad who suffers a fatal wound from flying debris during the squad's first major urban combat mission.

Poundcake is a quiet, eight-year-old member of the child soldier unit, enduring the grueling realities of boot camp alongside Ben and Ringer.

Teacup is the youngest member of Zombie's squad, a seven-year-old girl who tightly clings to her assigned assault rifle, symbolizing the tragic loss of childhood in the apocalyptic world.

Megan is a young survivor who bonds with Sammy while being transported to Wright-Patterson. Having lost her entire family, she is separated from Sammy upon arriving at the base after failing a medical screening.

Parker is a soldier who manages the transportation of children to Camp Haven. He maintains a friendly facade to keep the terrified children compliant.

Chris is Ben's tentmate at Camp Haven. He is unknowingly used by the base's medical personnel as a test subject to manipulate Ben into proving his loyalty.

Lizbeth is Cassie's best friend before the arrival of the aliens. She is a typical teenager who encourages Cassie to confess her crush on Ben Parish right as the first wave hits.

The Crucifix Soldier is a wounded man Cassie encounters while scavenging. His tragic encounter with Cassie highlights the deep paranoia and breakdown of trust among human survivors.