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 left the palace because she saw no future for herself and Prince Tenyou. But now that the imperial princes are working together to improve the lives of Ajin in the kingdom, Rangetsu once again has hope. She even passes the difficult imperial military exam to become the first Ajin to be granted an officer's rank, earning her the right to return to the palace and Prince Tenyou's side. But not everyone is in favor of the changes. Will increasing tension with the neighboring countries make war inevitable?