Kanata Satsuki 
The Emperor’s Lady-in-Waiting Is Wanted as a Bride (Manga) Volume 3 [EPUB ebook] 

The emperor’s condition is worsening, and the mana warping is beginning to affect the other imperials as well. Lyse, Sidis, and Alcede are doing their best to search out the cause of the incident, but time is of the essence. The mastermind seems to have a connection in the palace…or is something even more nefarious afoot? Lyse is determined to get to the bottom of it, even if it means risking her life again. Will she be able to keep everyone safe AND keep her true identity a secret? It may turn out that she’s not the only one hiding who they really are…