The Gatekeeper by K. Alex Walker

Cocky. Selfish. Arrogant.
Immortal.

Chief Mataio Tauati took over his father’s post as Lord of The Underworld at just seventeen years of age, mere weeks after his father’s passing. Twelve years later, he’s become the strongest god of his ancestral lineage. To challenge him is a death sentence and, for the most part, everyone understands the rules–no one defies the Lord of the Underworld.
For the most part.
Archaeologist Tia Coleman seems hell-bent on proving herself as the exception.
He refuses to believe this woman who isn’t afraid to challenge him and doesn’t do a thing he asks is supposed to eventually be the reason his heart beats. Being the strongest means there’s no room for weakness, no matter how much she softens him, and there’s no room to be vulnerable, no matter how easily she brings him to his knees.