Why he hired him is still a bit unclear but I think it was to keep juheon’s aunt away from dohu and to also keep an eye on dohu but I think this happened once juheon returned, before it was to dig up dirt on his aunt.
And the new villain persay the one who beat up dohu is dohu’s highschool bully dohu juheon n bully also met at the university festival before, but I don’t think juheon had any idea about him being dohu’s bully but Pi did (?) and thats why juheon is mad at him.
This is what I remember, if you reread it let me know how much if this is correct

Now I have to reheat this whole season because I forget who's who