La bestia del rey, 1

Since time immemorial, the ajin have been born to act as servants and guardians of their masters, but as soon as they are no longer useful they are eliminated as mere spoils. Rangetsu's twin brother, Sogetsu, was forcibly taken away by the Imperial army to serve as Prince Tenyo's servant, but he is killed in one of the dynasty's bloody feuds. Driven by hatred, Rangetsu swears to take revenge on her and eliminate the man who killed her brother with her own hands. To do this, she must impersonate a man and infiltrate as one of the palace's servants.