Mystic Nine

the vibe/setting is similar, and some parts of the story in mystic nine felt similar to gyeongseong creature. i can't tell you too much about it, or I will spoil it ;)

All three iron triangle characters remain the same as well as the actors. It has both Republican era and modern age understanding.

The Mystic Nine is the story before The Mystic Nine against the Coming Storm. You must watch it before The Mystic Nine against the Coming Storm to understand it more

These are the similar types of the series, basically in the same universe, both the same creator Nan Pai San Shu.