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!

As Rangetsu and her unlikely allies follow whispered rumors through the palace in search of any hint of her brother, she finds it increasingly difficult to keep from spilling her own secret to Prince Tenyou. But revealing her true nature will upset the uneasy accord she has built between them. And even worse, it might interfere in her desperate hunt for Sogetsu!