Most people think the Hunger Games has only 2 antagonists; Coin and Snow. The interesting thing is there are 3 the issue with the 3rd character is she belongs to 3 sides: The Capitol, The Rebels and her own. Yes, I'm talking about Katniss. This is really confusing and I don't know if I can really explain it that well but I'm going to try.
During the series she takes on 3 identities:
-The Girl On Fire
On onside of the series you have President Snow, who controls the Capitol and The Hunger Games which include The Girl on Fire since she's part of the show. That puts her on one side.
Then you've got Coin, who controls 13, who leads the rebellion this includes The Mockingjay. She again is on the enemies side.
And then you have Katniss, no role, just Katniss. Who belongs to her own side away from both the Capitol and 13.
In the roles of both The Mockingjay and The Girl on Fire the enemies control her she is not herself in fact she against herself. The enemy within the enemy you could say.
Also during the entire series she never does not have a role: She is the girl on fire until she becomes the mockingjay. And what happens after she is neither the Mockingjay or Girl on Fire? She is nothing because she's become to broken to be herself, so she becomes the shell-shocked lunatic that they all deem her as.
I don't know if you understood that but what I'm trying to say is Katniss is always against herself in the story. She really is both the main protagonist and antagonist of the story.