Law of Harmony Set inaccessible

Hello! I've been playing for about 2 weeks now and managed to get Qiuyuan and I think I have a general idea how builds in this game work, BUT his recommended set - Law of Harmony - is in an area I can not access yet.

I'm in act II, Act III, and I've been kinda grinding the story just to be able to get to his set, but it's getting a little frustrating since there's always a Fog that kicks me out...

Is there a sidequest or something that I'm missing or do I really have to brute force the story up to a certain point to use this character?