it is just a small wheel in the events to unfold. Basically the lingering shadow that is going to engulf Jinshi and Maomao soon.
Even though it is a season's end it will only be the opening act to the whole story.
Or talking in light novels, this should be somewhere at the start of LN 5 /16 and the story is ongoing and the arc starting now will only be concluded somewhere in 14 or 15 iirc.

The fortress arc was so underwhelming. Even their reunion was lackluster. Idk, am I the only one disappointed? I was hoping for so much more