A Stranger Things - KH Divergence parallel I'd not picked up on.
In my KHIII rewrite, the eldritch demon god who is progenitor of all Darkness in the World, Darxomnious, is officially unveiled as the Greater Scope Villain of all KH lore to that point, having been imprisoned within a black box along with the pieces of the original X-Blade but from there his darkness was able to influence the man charged with looking for the box, Master Luxu, so that Luxu let him out and eventually transferred him into a new Dreamscape prison tied to Luxu's own heart, an act that went about as well for Luxu as what Sailor Galaxia did with Chaos in Sailor Stars. Darxomnious gains more sapience and intelligence from Luxu, ultimately hollows Luxu out and drives him mad so that he becomes his vessel. To compare and contrast with Stranger Things, this is like if that scientist with the briefcase carrying the alien rock had been overtaken and possessed by the Mind Flayer and he became the first Vecna. The one time Luxu is seen free of Darxomnious' control within the Final World, he has become so completely dependent upon Darxomnious for life sustaining power that he chooses to re-embrace him.
But the parallels don't end there, because it turns out that Xehanort - as in old Master Xehanort who'd eventually take Terra as his vessel, lose his memory, and become the man who'd be split between a Heartless and a Nobody - was influenced at a very young age by a fragment of Darxomnious that entered his heart through the Dreamscape, beckoning him to go see the larger World and delve deeper into darkness ("Find Me!"), which gradually fucked him up and turned him into the sociopath he was. Xehanort wanted to shape his own destiny, to be a part of something greater than his own tiny world and even become something greater than human, but to Darxomnious, his destiny was always to be just another vessel for him. Sora doesn't exactly go "It wasn't you. It was never you!", but he might as well have since he does extend empathy for Xehanort and plead with him to let Darxomnious die when Luxu has been slain and it's come close to that, so that his heart can finally be free of that darkness....but Xehanort, without hesitation, beckons Darxomnious into himself, his essence merging with him in order to become this story arc's Final Boss. ("I need it, and it needs me. We. Are. One!")
Also note that I came up with this years before ST5 came out!
Say what you will about the Duffer Brothers as writers (which they certainly falter as compared to being directors), but in terms of storytelling instincts, they will forever have Tetsuya Nomura beat.
