Violet:
I have been waiting for you, Heroes. Leona Blackbird and the advance parties have built strongholds and are waiting for your aid.
Go to Sayunes and select one of the squads, Leona Squad, Sporcha Squad, Elikia Squad, and Devianne Squad.
It was reported to me that Sayunes is well hidden inside the castle. If you destroy Embryo Castle Siege Tanks or Embryo Castle Magic Tanks, one of the Embryo Commanders will appear. If you defeat the Embryo Commander, Sayunes will show up, and you'll be able to move to the next area through it.