The tunnel under the Moonveil Palace was dug under the secret orders of Aurora. No one, not even Sera, knew about this, for this was something Sera had decided clearly on her own whim and for her own personal reasons.
An escape from Tesarius.
When her knights first learnt about her distaste for the Emperor, they were shocked. They believed the greatest thing a girl can dream of is becoming the Emperor's lover, so when they learnt that person was their own Commander, they were genuinely rooting for her. Yet, after their findings, they couldn't help but think a second time. Why would a person like Aurora, someone they see as a divine angel, not share the same dream as other girls? Unless something is brutally wrong with this said Emperor?