But I'm a theory enby myself, so I'll kick it off with some o' those:
On the nature of Nobodies and beings in general:
Ansem The Dumbass says that it is the STRENGTH of one's will that determines whether they'll become a Nobody. The man being wrong about Most Things, this isn't quite the case. I believe it's actually how MUCH of one's will exists outside of their Heart, and what that will entails determines their exact form, even being able to be shaped by the will of another in some cases.
Creepers have nothing left but the will to keep moving, Dusks have the will to continue being, the other types of Nobodies encountered in KHII are shaped by the wills of the Org members, and the Org themselves have the entire will to continue being themselves. There's also Xion, very susceptible to the will of others in her form (her face looking different to everyone early on) and then gaining a will to return to Sora so strong it overrode her entire physical form. I could talk about other Nobody boss forms but I can sum that up with "the will to utterly destroy your opponent" being strong enough to alter one's form.
This isn't exclusive to Nobodies, however. I believe ALL physical forms in KH are shaped by will, however this will is normally provided in ample amounts by the Heart. This is why Heartless take Hearts to give themselves form, they require the will contained therein to exist in the worlds of light. Unversed take strong emotions, Dream Eaters take dreams and nightmares, both also being potential sources of will.
The idea of Hearts shaping one's form through will also brings me to the cases of Ansem Seeker of Darkness and Sora in KH1. Xehanort is a very willful being, so much so that not only does his Nobody contain enough will to keep his human form, but his Heart contains enough will to completely override the normal takeover of darkness that occurs with Heartless, something very rare. Sora on the other hand I believe has his ENTIRE will contained within his Heart, his Nobodies instead being the will from outside the Hearts of Ventus and Kairi while they were in Sora's body. Thus, since Sora was within the Shadow that absorbed his Heart basically in his entirety, his will was able to override the takeover in a manner similar to Ansem. (Take that, KH wiki. "Somehow" my ass.)
Lastly, I'd like to discuss how Nobodies continue to be Nobodies despite the fact we know they can grow new Hearts through personal connections. They remain Nobodies because the primary will shaping their form remains that which lies outside their Hearts.
Side note: Lingering Will fucking rules because the will just clings to itself without so much as a body. I suppose it counts as a Nobody under my definition but I prefer to liken it to an Undertale Determination ghost.
They already told us what Kingdom Hearts is no seriously I'm not joking:
While they always discuss Kingdom Hearts in vague terms, it is not as if we are bereft of clues as to its nature. We know it's made of many individual Hearts, there can be and are multiple Kingdom Hearts, they act as collective Hearts of a set of worlds, and access to them provides a sort of power over all the worlds that Kingdom Hearts connects.
Is it really fair, then, to say we have no idea what Kingdom Hearts is? Emotional connections are shown time and again to have incredible reach, and how many such connections do you think the Hearts within Kingdom Hearts have? Those connections ARE what makes a Kingdom Hearts the Heart of many worlds, those emotional ties hold the worlds in a single cohesive space and prevent them from spiraling out into isolation.
This explains why control over one is inherently dangerous, the connections give one direct access to all the worlds the Kingdom Hearts acts as a Heart to. One could cover those worlds in darkness, distort them, sever them, all bad! It's something no one being should be trusted with.
...All that said, the games COULD have stood to be a bit more direct about it.
BONUS: Who or what is Twilight Thorn?
Spoiler!
