Prisoner of Steel and Shadow by Meg Anne

A Kidnapped Queen
A vengeful god has stolen everything from the queen of assassins. Her title. Her power. Her memories.
Even her name.
Now merely a ghost of her former self, Shadow must enter a deadly game and fight for her freedom or risk spending the rest of her life as a madman’s prisoner.
But, in order to win, she may be forced to lose what’s left of her true self in the process.
A Legendary Warrior
Resolved to a life sworn to duty instead of love, Ronan wasn’t prepared when the assassin queen swept into his life. Then as suddenly as she appeared, she vanished without a trace.
After five years he’s no closer to finding her, so when a prophecy offers the first clue to her whereabouts, there’s no question he’ll set off to rescue her. But when they finally come face to face, she has no idea who he is. In fact, she seems more inclined to slit his throat than fall into his arms.
When it becomes clear his only chance to save her is to become her enemy and enter the contest, he doesn’t hesitate. He’d risk everything to bring her back.
Including his life.
After all, the only reason his heart still beats is for her.