Blood Union: Part One by Vela Roth — book slip

Cassia is ready to embrace her eternal future with Lio, becoming an immortal Hesperine and fulfilling their Grace bond. However, an unexpected revelation about the past sends them on a perilous journey across the Empire. As they seek out dangerous truths, Lio is determined to protect Cassia, even if it means risking everything he has worked for as a diplomat. Their love is tested by political machinations and ancient secrets that threaten to pull Cassia back into the human world.

For fans of steamy romance and classic fantasy worldbuilding.