Sky in the Deep by Adrienne Young From Goodreads: Raised to be a warrior, seventeen-year-old Eelyn fights alongside her Aska clansmen in an ancient rivalry against the Riki clan. Her life is brutal but simple: fight and survive. Until the day she sees the impossible on the battlefield—her brother, fighting with the enemy—the brother she watched die five years ago. Faced with her brother’s betrayal, she must survive the winter in the mountains with the Riki, in a village where every neighbor is an enemy, every battle scar possibly one she delivered. But when the Riki village is raided by a ruthless clan thought to be a legend, Eelyn is even…