You are reading the definitions as "good guy" and "bad guy", when I'm defining it as plot reactions.
Antagonists drive the plot forward usually with plot devices. For example, evil guy with a doomsday machine.
Protagonists react to the plot devices. For example, good guy going to stop the bad guy from using said machine.
Now, the roles can be placed to either villains or heroes. Doesn't matter. The label is given to who is driving the story forward, and can be the opposition or rival to the main character, just doesn't have to be.
Jayce, is currently an antagonist, no idea how he will match up in the rest of things. But from what we know with this arc, he is a antagonist.
You have to look at story arcs individually, with only a few components from the last one being pulled over.
For SB, this Ginger/Licorice is the main villain, and her agents have been responsible for the movement of the previous arcs. She's the same way in Melancholy, which is unconfirmed to be a sequel, reboot, or a side story. Thus you should be very careful when it comes to dragging what information across. I am combining the girls right now because they have yet to develop independent bodies, and because we still have no idea what Licorice is.
To continue your story idea, people switch roles all the time, and it does matter on what they are doing at the moment of the story. For example, Vegeta from Dragon Ball Z is regarded as a enemy for most of the beginning of the story, and switches from being an antagonist to a protagonist while on Namek. Through out the rest of the series, he rotates back and forth between the roles. Heroes who are usually protangonists can become anatagonists when they create a trap or an offensive plan against the enemy.
So, your point is null and void.
EDIT: I'm sorry, I didn't mean to come off sounding so much of an asshole. I was thinking more about this post today and thought it was way too mean, so I'm sorry.
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