Sovereign Oathbound by Caelia Bevanor

The kingdom of Elemyr has never been ruled by one.
A representative of the Land. A representative of the Sky. The heir of the reigning Trinity, bearer of the Sea.
Three are bound in sacred rite. Three must endure the trials of the elements before they claim the crown.
When Vonetta Sage is chosen by the spirit of the Land, she is torn from the only life she has ever known.
In her place waits a prince shaped by legacy and a scholar who never wished to leave the quiet of his cloistered home.
They are strangers. They are bound. Across the forest, through storm-torn waters, and into the mountains where the air grows thin and merciless, the Trinity must prove what their vow demands:
no secrets. No betrayal. No division.
But vows spoken before the Gods are one thing. Choosing to live them is another thing entirely. In Elemyr, sovereignty is not inherited by blood. It is forged—between Three.