Alternate Character Interpretation: Ami encouraging Ji-Soo to make a move and get Jin-Ho: is she still trying to pull the strings to make someone else take Jin-Ho out of her way to Hae-Young, or does she really care about Ji-Soo and is trying to help her get rid of her doubts and inferiority complex? You be the judge.
Mary Sue: It's implied that some of Ji-Soo's classmates dislike her because she's good at athletics, has good grades, and a lot of guys find her attractive (we don't get to see much of this thanks to the kind of teachers in her school, though).
Moral Event Horizon: The infamous No-Holds-Barred Beatdown Jin-Ho gave to one of his female classmates upon finding out she and other girls picked on Ji-Soo. Some people see it like she deserved it (Ji-Soo's face ended up all beaten to a pulp for trying to fight back against three girls and they striped off her skirt). Some other people thought Jin-Ho lost a lot of character value after this (up to the point of stop reading in some cases) because he was never called back for hurting a girl (of note here is that the same characters Jin-Ho stood up for told him he went too far by the way). The bullies themselves just took it as it came (the leader of said gang said it was fault of the bully girl in the first place, even when he told them not to pick any fights just for the sake of it)
Ship Mates: Ami realized that she would greatly benefit form shipping her friend Ji-Soo and her love rival Jin-Ho. And so she did.
It's worth pointing out that the school faculty punished Jin-Ho by caning.