Stolen Mayfly Bride by Sarah K. L. Wilson

Sometimes stealing a life is the only way to save it.

Elkhana is the Mayfly Seer. Ripped from her family, drowned, and set into a magical cage, she lives only one day a year to tell fortunes for her former people.
When Vidar meets her, he sees a resource he can use to save himself from his enemies and the torturous demands of his own liege and court.
But the bond between Elkhana and Vidar is growing. She’s slipping into his dreams and changing how he sees the world and he doesn’t know if he can keep on using her now that he sees her as a person.
Without her visions, he’s powerless against his enemies, but if he has the chance to steal her away from her cage, shouldn’t he take it?
To succeed, he’ll need a plan, a lot of nerve, and all the bargains he can strike. Will it be enough?