Phantom thief Rosenkreutz, who disturbs the great power of Fahrenheit. His true identity was Cecil, the son of the current emperor's mistress, the Marchioness of Hanover, with her ex-husband. He hides his gender and marries Oscar, the Chancellor of his neighboring country of Aquitaine, as a substitute for his poisoned half-sister of imperial blood. Cecil had suspected him as the mastermind of the assassination, but gradually became attracted to Oscar's humanity. 1z2xw
8 Volumes (Complete)

Cecil's sister renette has been murdered now Cecile must act as her sister to find out if renette's fiancé was the one who did it. This is all I know from what sites like kissmanga and mangaeden put up on their site.
Despite the great artwork and great ideas in this work, the first chapter so far is very disappointing because of how confusing the organization is. We are only at one scene, but we get thrown into several flashbacks or to other characters.