Hunted by the Demon's Vow Book by A. N. Caudle

Vhaena is betrayed by her own town and sacrificed to "The Hunt," a brutal seven-day survival trial on an isolated island populated by vicious demons. Daemon, her brother's best friend and a secret demon hiding in plain sight, enters the island to protect her due to a binding oath. Together, they must survive the deadly terrain while fighting off external monsters and the dark, predatory pull of their forbidden attraction.