Deathbringer

Rumelt is a normal town. Or as normal as a town can be when they're cut off from civilisation. They live in perfect harmony and have nothing to fear--apart from the Deathbringer, who lives in the underworld and steals the strongest, healthiest teenagers away to their deaths.
Beatrix has lived in Rumelt her whole life. She has nothing to fear from the Deathbringer, being the weak, sickly teen that she is. She knows that. Everybody knows that.
But on the eve of her 15th birthday, she is stolen away, never to return home again. She encounters the Shadowland, a near-perfect copy of Rumelt, save for the fact that it's underground, and is the base of the underworld. When she arrives, she is given a choice: die, or join the Deathbringer's army. Choosing the latter, she meets Jamie, a 16-year-old half-elf boy with a mysterious past. Jamie has his own secrets, but perhaps he can help Beatrix discover the secrets of the Shadowland, and of the Deathbringer himself...