Lazulis Castle: Grand Hall
When you go into Seek mode, look at the black knight to the right of the main staircase.
Dagran will hand over the Key Item: Castle Pass, which will let Zael go in and out of the castle.
After the scene, Zael will be free to move about the Grand Hall of the castle. There is a Library on the third floor on the left but everything else is closed off at this point except for the door in the middle of the 2nd floor. A guard will ask you to head through it when you approach.
During the scene, look at Syrenne during Seek mode.
Zael will see Therius and General Ashtar in this fairly long scene.
Talk to Syrenne and overhear a conversation between Therius and Ashtar once control is regained.
There are continuations to some other side-quests while in the castle.
Back in the main hall, Dagran is on the 3rd floor choose the left option when talking to him to advance to Chapter 9.
This is your last chance to do anything in Lazulis City until the conclusion of Chapter 19. Zael can still come in and out of the castle before this point.