While still in act 5, after you get the message about the airship from another country, go south to find the airship and interact with it once. It only appears in act 6 when you interacted with it in act 5.
thanks a lot! I didn't notice the airship, my bad.
Tsubaki's mother? She is in one of the bedrooms in the top right of the building with the bar and the expedition guild in Cloud Haven.
