The "Undying," beings created from the remains of fallen soldiers, are nearly immortal entities built solely for combat. When the war concluded, they were deemed unnecessary, prompting the Church to launch the Undying Hunt, a systematic campaign to eliminate these creatures. Eighty years later, only a handful of Undying survive, still relentlessly pursued and destroyed by the Church.
Kieli, an orphan enrolled in a religious boarding school, has a unique gift: she can see spirits. Ostracized by her peers, she spends her days conversing with Becca, the ghost of a girl who once lived in Kieli's room. One day, Kieli encounters Harvey, a distant and enigmatic Undying, one of the few still alive. After an unexpected incident, Harvey saves Kieli from a train accident, risking his own life in the process. Driven by curiosity about Harvey, Kieli chooses to join him on his journey to fulfill a promise made to the Corporal—the spirit of a fallen soldier now inhabiting a radio—to return his mortal body to him.
As they travel together, Kieli comes to see that beneath Harvey's aloof exterior lies a kind and caring soul tormented by memories of war. Through their interactions and growing bond, a lasting connection forms between them, offering Harvey a chance to rediscover the humanity he had lost.
