Song Ji-hyo's involvement may be disappointed to learn that her role as the titular witch Hee-ra is obfuscated. We know she's been out of the wish-fulfilling business for awhile and she wants to get back into it again. It's not clear why. I was also never particularly interested in learning the reasons for this, as Hee-ra is too engimatic to really work as a perspective character.
That role more falls to Jin (played by
Nam Ji-hyun), who has boldly endured company life for several years and finally decides to make a change, albeit not a willing one. Jin isn't unsympathetic but as was the case with Hee-ra, I was disappointed with her lack of particularly compelling motivation. It's only right at the very end that Jin has a clear goal, and her desire for magically enforced revenge lacks bite.