I’m still have trouble getting a handle on your concept. (And ditto with you on the angle I pitched.) A fundamental problem is that the world want to dramatize only exists in your head. That’s not your fault, of course. It’s the nature of the challenge frequently presented by sci-fi and fantasy genres.

The reference to Plato and Jung was a mistake for the purposes of this thread. But at least I can point to cultural and literary references for my version as a hook on which to hang the idea. I can say “It’s something like this” to help people grasp the concept.

Is there a pop culture or literary reference you can point to and say: “this story is something like this” that will help me and others to grasp your concept?

You have in mind the notion of a doppelganger. That’s an excellent idea. It’s been used a number of times in stories and movies. Now, why is that? What is the hook in the idea of a doppelganger that makes people want to write about it? The hook that makes YOU want to use it in your story?

It seems to me that the hook for the writer (and audience) is the situation of a person meeting his mirror opposite. That is the only aspect of your story that hooks my interest (in case you hadn’t noticed). All the other powers and abilities maybe be Interesting — but I don’t think they are as compelling as the idea of a High Noon showdown between a protagonist and antagonist who are mirror opposites.

So why do you want to make the antagonist one part in the doppelganger relation —but give the other part to a supporting character?

If the core conceit of your story is that of a doppelganger, than it seems to me that the protagonist ought to be part of the core conceit, the character who is confronted, threatened by his doppelganger. Not a supporting character. IMHO, it’s too potent of a dramatic technique to assign it to a supporting character. The protagonist should own it, and the central conflict that results.

(And if the doppelganger is not the central gimmick, imho, it ought to be.)

The central conceit of the “Star Wars” franchise (and you’re hoping for a franchise out of your idea, are you not?) is the Force. Which George Lucas did not assign to a supporting character, not to Han Solo, not to Chewbacca, not to the droids, not even to Princess Leia (a sexist lapse, imho). He assigned the Force — all its potential power and all its potential danger– to the protagonist, Luke Skywalker. And to his mortal adversary, Darth Vader.

The Force is the Big Idea, the gimmick, the organizing principle, the hook, the sizzle AND the steak for the entire “Star Wars” franchise; It’s the gotta-have in every plot of every episode.

You wanna build a franchise? What is your Big Idea, your central gimmick, akin to the Force, the gotta-have that will be central to every episode of this franchise?