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!

Now that Rangetsu has her brother safely back, she can finally relax after years of revenge-fueled vigilance. But her peaceful days are anything but restful. Without the fiery urge for vengeance to distract her, the terrible disparity between the treatment of humans and Ajin has become even more painfully clear. Can she really be content to stay quietly at Prince Tenyou's side when the world sees her as less than a person?