V.E Schwab 
Shades of Magic 
The Steel Prince #4

Hot-headed, arrogant, and untested, Maxim found himself in Verose, better known as the Blood Coast, and up to his neck in trouble. Determined to make a name for himself and assert the power of the crown in this insalubrious backwater, he fell in with the local garrison, and was taken under the wing of Isra, an experienced if battle weary soldier.Skilled in the illegal art of bone magic, Arisa rules the Verose with a violent fist. Isra is both her niece – and the only survivor of the Verose garrison’s attempt to wrest control back from the Pirate Queen. But Arisa has overreached. Seeking new members for her crew, she has announced a fighting tournament, with the winner gaining the right to face Arisa in combat.As Isra predicted, she must defeat Maxim in order to face off against her aunt, Arisa the Pirate Queen. Using all her expertise, Isra bested Maxim in single combat, and took the prize.