Damn, I messed up again, as always: I immediately headed to Svetlana, and as a result, I was being attacked by demons, orcs, and sometimes necropolises. With Anastasia, I killed Sharka and some other orcish heroine, but it doesn't say that the orcs have been defeated. Svetlana tried to attack the demons, but it was hopeless... In short, I plan to clear the entire island and then go to defeat the demon with Anastasia. Svetlana is currently managing to hold back the secondary demons.
If that doesn't work, I'll have to replay according to your plan, Winner :)