wrote this in response to a tweet but decided not to bother
This is my opinion and am not claiming to be the sole person to have ever considered this idea. Also SPOILERS FOR KINGDOM HEARTS 3. Moving onto this tweet reply that became a half baked micro essay:
In my biased opinion, to me it looked like the game was focusing a lot on sora and riku, in the form of sora and co making several references to riku throughout the first half of the game.
Towards the end of the game, we are shown several scenes focusing on sora and kairi. They are relatively overt (holding hands, hugging, protecting each other), and seem to allude to a potential romance between them.
And then we reach the ending. Kairi cries. Sora disappears.
I see this as almost a metaphor. Without even considering the possibility of a romance between sora and riku, the game shows us that a future relationship between Sora and kairi is unlikely. The game rather suddenly plays up the romance between sora and kairi with all of those sora/kairi scenes. It practically shoves it in our face, only to pull them apart at the end.
This isn't even like the ending of the first game, where sora and kairi promise to meet again. In kh3, sora *basically* dies (it's a disney game). But kid-friendliness notwithstanding, sora's disappearance is very definitive, to the point he can't be found after a year of searching.
In the game world, this literally means there is to be no reunion between sora and kairi, or anyone else to be fair. To the audience, this represents how the pairing we were shown towards the end, the pairing that is therefore at the forefront of our minds, is not meant to occur. Not meant to be.
TL;DR: kh3 shoves sokai in your face in a mega blatant way then kills sora. Very obvious metaphor.