The world shared by humans and ajins (those who are half beast and half human) is not paradise. On the contrary, humans rule over ajins with strictness and contempt, using them at their own convenience: men as soldiers for their special powers and women as prostitutes, downgraded to the lowest rank.
To change that destiny, Kogetsu serves the king under the guise of a man.
Story set in the same magical world of "Reimei no Arcana".