Cassie is a 16-year-old survivor of the alien invasion that decimated Earth's population. She possesses a stubborn streak and deeply values her emotional connections, especially her love for Evan Walker. Her dedication to her younger brother drives her to take immense risks. Unlike her militarily trained companions, she relies heavily on compassion and instinct to survive.

Ringer is a 17-year-old expert marksman who lost her father during the plague wave of the invasion. She relies on cold logic and tactical detachment to stay alive, often viewing survival through the lens of a chess game. She struggles to understand Cassie's emotional choices and prefers to operate independently to minimize risk.

Ben is a 17-year-old former high school football star who led Squad 53 during their time at Camp Haven. He suffers from a severe gunshot wound that limits his physical mobility. Despite his injury, he maintains a strong sense of duty to protect the younger members of his squad.

Evan is a Silencer whose consciousness awoke in a human body when he was thirteen. His deep love for Cassie causes a massive internal conflict with his alien identity. He possesses enhanced physical abilities but finds himself stripped of his usual strength due to severe burns and broken bones.

Colonel Vosch commands the military forces responsible for training child soldiers. He utilizes sophisticated psychological warfare to break down the will of human survivors. He is ruthless, intelligent, and views human beings as expendable pieces in his larger extermination strategy.

Sam is Cassie's young brother who was recently rescued from the child soldier training facility. He is heavily influenced by his military training under Ben and exhibits flashes of aggression. He desperately seeks stability in the chaotic ruins of the world.

Teacup is a seven-year-old girl and former member of Squad 53. She is terrified of the rats in the hotel walls and clings fiercely to the older survivors for safety. Her impulsive decision to follow Ringer places them both in immediate danger.

Poundcake is a quiet, traumatized boy who serves in Squad 53. He earned his nickname by carrying a piece of cake in his pocket when he was taken to Camp Haven. He relies on his silence and weapons training to cope with his immense grief.

Dumbo is a young member of Squad 53 who functions as the group's medic. He checks injuries, monitors the perimeter, and strictly follows the chain of command.

Grace is a Silencer who met Evan when they were teenagers discovering their alien consciousness. She is highly lethal and views human beings with predatory contempt. She collects trophies from her kills and remains completely devoted to the eradication of humanity.

Razor is a young recruit stationed at the military base where Vosch holds his prisoners. He behaves coldly at first but slowly interacts with Ringer over games of chess and chaseball.

Megan is a young survivor who traveled on the same transport bus as Sam. She arrives at the survivors' hideout confused and complaining of a sore throat, bringing an immediate, hidden danger to the group.

Dr. Claire is a medical professional working under Colonel Vosch. She administers agonizing experimental injections to prisoners and displays a cold indifference to human suffering.