The Prince Is A Girl: The Beast King's Captive Mate

In the Dark Age, Princess Emeriel disguises herself as a prince to survive. To save her sister, she becomes a slave to the Urekai and discovers she is a rare "Siren" capable of mating with beasts. Chosen by the High King Beast, berserk for five hundred years, she navigates fear, desire, secrets, and soul bonds as fate pushes her toward the abyss.