Have Himika (Miko), Olivia (Priestress), Oboro (Ninja), Arwyn (Elf), Julian (Warrior), Reiris (Knight) and Maia (Thief) by your side before attacking Easendork (the City before the tower on the west). To be sure, all of those must be deployable in the dungeon.
If you're done, attack Easendork...