Nightrender

Kingdoms will fall, gods will die, and hearts will be broken in this sprawling new fantasy from New York Times bestselling author Jodi Meadows.
"INTRICATE... UNIQUE... COMPELLING."—YA Books Central
In the middle of nothingness is the Island of Salvation.
Reality bends easily here. Villages disappear. Forests burn forever. Pockets of inconsistent time are everywhere, their boundaries strung with yellow ribbon. And the three kingdoms of Salvation have been at war for a thousand years.
But the greatest threat is the Malice, an incursion from the demon plane slowly tearing its way through the world's weakest seams. Seams that—once split—will lead to the total unraveling of night and day, light and dark, life and death. 
Not that the human world takes much interest. Of more concern is the upcoming marriage of Rune Highcrown, Prince of Caberwill, and Johanne Fortuin, Princess of Embria—the serpent bride, a girl of famous cunning—which offers a possible end to the ancient conflict. But Rune has noticed the growing darkness, and he is determined to summon mankind's only defense: Nightrender, the hammer of the gods, an immortal warrior more weapon than girl.
There is only one problem. The last time she was summoned, she slaughtered every royal in Salvation, and no one knows why. Will she save humanity from the Malice... or plunge it deeper into the fires of eternal war?
A YAVA Award Nominee!
"Tantalizing."—The Bulletin of the Center for Children's Books, Starred Review
"Lush."—Publishers Weekly
"Wild."—Booklist
"Rich."—Kirkus Reviews