Courting War by Hazel St. Lewis

The number one rule in life: never make a deal with Death…even if Death is your sister.
Theodra, Goddess of War, knows not to break this rule. But like all arrogant gods, she does just that. Unable to hold back, she destroys a ship full of traffickers, unaware there are girls on board. When one of them dies, Theo trades with Death for a soul she will someday love. A soul for a soul. A good deal, in her esteemed opinion, since she is incapable of falling in love.

Unfortunately, Theo might have been mistaken.
Thirteen years later, as a punishment for killing too many wicked men, she is sentenced to play as a mortal in a deadly tournament called The Sacrifice. The games are played in pairs, and her partner is the sinfully handsome Prince Kellyn. Even though they despise one another and can barely work together, sexual tension burns between them. But if their hatred turns to love, it will cost Kellyn his life, for Death is always waiting to collect.