Ajin boys who show signs of special abilities are conscripted to serve in the imperial palace as beast-servants--status symbols and shields for their royal masters, to be kept or discarded on a whim. When they were children, Rangetsu's twin brother Sogetsu was ripped from her arms and sent to the palace to attend Prince Tenyou as a beast-servant, where he quickly fell victim to bloody dynastic intrigues. Now in a world that promises only bitterness, Rangetsu's one hope at avenging her brother is to disguise herself as a man and find a way into the palace!

Rangetsu loves Prince Tenyou deeply, but she knows an Ajin beast-servant and an imperial prince can never be together. The best thing she can do for both of them is return to her rural hometown. But months later, Rangetsu has a sudden surge of hope when Taihaku arrives to drag her out of retirement to help Prince Tenyou achieve his lofty goal of improving the lives of all Ajin. Is there a chance for their love after all?