Spoilers!!!
Rose and Agnes are the same person, she just lost (suppressed her memories) and (Anges) is originally from a fallen family and she is plotting to kill the emperor, that's why she became his concubine (Also she wanted to make her lover, the blonde headed dude the emperor). So in the end the emperor tells Rose that he knew and he is hurt but still wants to be close to her, but she has to promise no more secrets and yeah pretty much she falls in love with him and yeah.
Two Names of Night