The Last Hunter - Pursuit (Book 2 of the Antarktos Saga)

The protagonist, kidnapped at thirteen, is thrust into a dark world beneath Antarctica, where they are trained by a hunter named Ninnis to serve the ancient Nephilim, a race of half-human, half-demon beings. After enduring a transformation that replaces their identity with that of a killer, they manage to escape into a lush underground cavern, living in fear of the Nephilim's return. As hunters close in on their location, the tension escalates, leading to a gripping confrontation that could determine the protagonist's fate.