story
surprisingly one of the simpler questions to answer. The Keyblade is the key that can open (or close) any door. And that was the theme of the first Kingdom Hearts: doors. the big villians plan is to destroy all worlds by opening the door to the Dark World and flooding the existing Light dimension with hoards of monsters. you also spend a lot of time closing off the doors to the heart of the world to protect their cores (monsters destroy core = destroyed world).
In addition to bashing enemies and being a large narrative hook, it's a nifty explanation for why you are able to simply tap on a chest and open anything you want. Or break and enter into a bunch of buildings (although the game forgets constantly that it can do that).
IP don’t make the game. The game makes the game.
There's a ton of people who apparently really liked Kingdom Hearts.
It's pretty elitist to consider some IP too sacred to remix.
I only know enough about what “Aqua got ‘Norted” means to put an apostrophe in front of ‘Norted. (Xehanort possesses people or whatever.) I also literally never saw Aqua in any game I played before KH3, except maybe as an extra I didn’t notice.
I was amazed.
Heh, not sure if pun intended but this made me giggle
If you're a teenager that may be much easier... or much harder, in cases such as yours.