Having only watched till episode 9, I got a theory or two on Seimei and Mansairaku.
I believe Seimei to be the one that plots to get rid of the old regime and implement a new regime for the benefit of the people but in a harsh and cold method. He would be the Machiavelli of the show ("ends justify the means"). We already know that he actually is not following nor giving in to the desires of the two ministers but rather working on plans that are out of the thoughts of the ministers (for example, both thought he concocted a cure for the Emperor when he actually served a strong poison).
Mansairaku on the other hand is the idealistic revolutionary that will bring doom to the country. His ways are likely to be too bent on the injustices served previously that it would merely turn into a vengeance drive (the ways he express the slights he feel and his haunting theme music). He and Seimei might be working to the same end of eliminating the old corruptness but their goals and methods would be different.
In this way, both in my thinking would serve as a good contrast and a nice mystery plot to go on. Who should Raikou support in the end? Destroy the corrupt regime along with the country or suffer a bit of slight of being servant to someone's plan to restore an effective government?
Of course, the above is just my opinion. They may be wrong.
