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 knows she must keep a low profile in the palace if she's to have any hope of tracking down her brother's killer. But when an Ajin is wrongly accused of murder, can Rangetsu stand idly by knowing that Prince Tenyou has the power to prevent another horrible injustice?