THIS IS ALL SPECULATION AND OH MY DAYS SO MANY SPOILERS!!
The Kingdom Key and Kingdom Key D are two unique blades the way that the x-blade was. They aren’t a representation of one’s heart, but constants that need to exist. This is probably because the x-blade was shattered or something. When the worlds became a realm of darkness and a realm of light, the KK was the light’s half of the x-blade and the KKD was the darkness’s half. They probably weren’t made from the x-blade themselves, but came to exist because of the state of the universe, much the way the x-blade did.
Anyway, KK and KKD are special. They reside in their respective realms to protect it. They have their own “consciousness” as it is, where they can choose their wielders. In my head, I always thought that they wouldn’t choose a wielder unless their realm was in peril. So when all the worlds start vanishing in KH1, the KK is like “woah hey what? damnit I better find myself a wielder”. It found Riku - one of few already anointed with using a keyblade - and I was like “sure this kid seems legit”. Then Riku went all darkness and the key was like “damnit, and I came all the way out here”. But he sees Sora, who has the heart of a keyblade wielder (Ven) and is like “actually this kid might work instead”. Then in Hallow Bastion it sees Riku again and is like “you’re that kid!” and goes with him. Then KK is like “actually you’re a dick and I like the other kid more” and goes back to Sora. And that’s the story of the KK.
So then there’s the KKD, chillin’ in darkness like “yeah man lovin’ this darkness gonna stay here forever” and then a mouse comes and picks it up. And the KKD is like “well, I mean, it’s been a while since like. I’ve done anything. Might as well.” and sticks with Mickey. But if it ever wanted to leave it probably could. Though I think the KKD and KK are both in this for the same reason: they want balance. Neither wants to see Light or Darkness consume everything. That’s why KKD stays with Mickey.
So, now let’s delve into keyblades as a whole. They were said to be “forged in reverence of the x-blade”, which is sort of weird since the x-blade looks dumb as hell and the keyblades look pretty rad most of the time. Maybe it’s like how an artist sees someone’s work and thinks “ha, I could do that, but better”. Anyway. “Forged” here is a pretty loose term, since hearts forge keyblades, but also like… you could just forge them out of metal, right? For the sake of simplicity and in the continuity of the franchise, let’s just define “forged” as “created with one’s heart”. This materializes a keyblade for the use of its owner. BUT it seems like whenever the owner dies, the keyblade can continue to exist. Since you know. The graveyard. This basically defies everything I know about creating and destroying matter but whatever.
So anyway. Wielders make keyblades with strong hearts. Are they blessed or something? IMO, it seems sort of like “forging a keyblade” was pretty damn easy before the world fell apart (KHUX). Maybe this is like a defense mechanism? Kingdom Hearts is like “well shit, I see what you guys do when keyblades are dime a dozen - you start wars! So you know what. New universe, new rules. No keyblades for anybody. Except these two new ones, KKL and KKD. No more wars. Stop it.” To which the very few keyblade wielders who survived the sundering were like “right, but how about we make a ceremony that lets us pass on the keyblade powers to new people, since like, we totally learned our lesson and won’t start another war”. So then the Ceremony came to be (which is just touching a keyblade apparently?? I think here’s more to it, but I’ll get to that in a minute).
So here we are in the new universe and we’ve got a few keys. The x-blade is broke, but that doesn’t matter until it becomes an essential and awkwardly convenient plot point. The KK and KKD are newly born. And I guess No Name (Xehanort’s blade in BBS and Master of Masters’ blade in Back Cover) survived, because why not. And then there’s the Dandelions. And that’s it. All the other keyblades are inert, since their wielders are dead. So someone passes the power of the keyblades onto Eraqus, Xehanort, and Yen Sid. Hopefully this gets revealed in KH3 since we got that awesome chess scene with chubby baby Eraqus. Yen Sid trains Mickey, then retires. Xehanort trains Ven, then fucks up literally everything. Eraqus trains Terra and Aqua, then dies. So we’ve gone from three to four wielders in one generation, since Eraqus thinks he’s special. I don’t know what “retiring” means in terms of using a keyblade, but it’s pretty safe to assume Yen Sid isn’t going to do anything but talk for the whole franchise. Xehanort takes over Terra. So we’re sitting at four wielders and six keyblades (since Terra/Xehanort each have one, and Aqua has Eraqus’s).
This brings about a whole other argument. Though the wielders die (Eraqus & in theory, No Name) the keyblades retain their power. Which is sort of in conflict with the keyblade graveyard. I think this has a lot to do with intent. Eraqus had always intended his keyblade to be passed down to Aqua in case he fell. MoM had always intended No Name to move forward through time. Each served their master’s purpose even after the master’s demise, so… in a way, they still had the heart of their master. I think this also explains why Aqua can’t summon her own keyblade anymore after the end of BBS. Her intent for her keyblade was to watch over Terra. It’s still doing that, in the Chamber of Repose. Then again, maybe keyblades can’t be summoned into the Realm of Darkness if they preside in the Realm of Light? Who knows.
Keeping the theme of intent, I think it has a lot to do with the Keyblade Ceremony. In every instance of the ceremony, the master intends to give the power away (Terra to Riku, for instance). So I think there’s more to it than just “touching the blade”. The only circumstance that defies this rule is Aqua to Kairi, but Kairi is a Princess of Heart so she can do whatever the hell she wants. So by the end of BBS, we’re sitting at six (potential) keyblade wielders and eight keyblades. Cue KK and KKD, makes ten. Actually, if we want to get technical, Xehanort might have been able to summon his own keyblade before being given No Name. So maybe eleven? At this point, the original Kingdom Hearts must be pretty pissed off.
So then there’s Sora. Who never had his own keyblade. Which I think is pretty cool. KK is Sora’s bro after KH1, so he never really needs one. And he was never given the ceremony officially. Though it could be argued that by housing Ven’s heart, it gave Sora the ability to have his own keyblade, but just the same it could be argued that once Ven’s heart is gone Sora might not be able to hold a keyblade at all. (I doubt that’ll be the case, but it’s funny to think about.) What are we at? Seven wielders, ten (possibly 11) blades?
Sora goes all sleepy time, so Roxas steals his Kingdom Key. KK is probably like “this is Sora! Feels like Sora. Probably Sora. I wish I had a glowing blue eye so I could be sure, but hey, whatever”. Xion “copies” Roxas’s key, explaining the two KKs at the same time. This is probably Ven’s keyblade since she’s siphoning parts of Sora out of Roxas, and the KK appearance is an illusion created from copying Roxas.
Xion dies. Roxas gets her keyblade (which was Ven’s). Dual wielding ass kicking ensues. Then when Sora wakes up, he can dual wield because Roxas - who is a part of him - unlocked that power for him. I think this is a really cool plot point actually, because it means when Ven gets his heart back, Sora will need to learn to manifest a keyblade of his own (not the KK) in order to dual wield again!! :D I’m all about Sora learning how to forge his own keyblade.
Let’s see. Lea gets a keyblade from Yen Sid’s ceremony. Bringing our total wielder count to eight: Destiny trio, Wayfinder trio, Mickey, Lea. Eleven keyblades: listed above (including KK for Sora), KKD (which means Mickey can probably dual wield), Master Defender (hopefully dual wielding Aqua in the future?!), and No Name (Terranort can officially dual wield..?).
Then keychains. Don’t worry, I’m almost done. “Keychains” modify the appearance of an existing keyblade. I actually don’t think keychains are actual keychains in most cases. It’s just that certain memories and experiences can color your heart, changing the appearance of your keyblade. The exception to this could possibly be Oathkeeper, since Kairi actually gives Sora a charm. But I don’t think he clips that thing on the end of his keyblade - I think just the memories of her and stuff bring about the transformation. Or maybe they are real keychains, but they are made when the heart remembers those memories? Because honestly, obtaining actual magical keychains seems absurd to me. This really isn’t elaborated on in any way.
Importantly, however! there are no keychains on the keyblades in the Graveyard. So maybe keychains are tied to a wielder’s heart, and when the wielder dies, the keyblade can be left behind but not the keychain itself. Again, there are exceptions with Master Defender (Eraqus) and No Name, since there is still intent in these blades. It’s interesting to think about. Also the Keyblade of Heart (forged from the seven princesses) doesn’t have a keychain. Maybe because it has no wielder? It’s a combination of seven hearts, rather than one? I don’t know.
ANYWAY. This was a lot longer than I wanted it to be, but I think about keyblades a lot. If anyone has anything to add or correct me on, PLEASE tell me because I LOVE TALKING ABOUT THIS STUFF!!! :D
You know I’m thinking of one of those old “characters meet their past/future self” scenarios with Riku and Sora and I’m laughing cause like
Okay okay first of all. Riku is consumed with self-loathing. Like he grabs KH1-Riku and just whispers “shut the fuck up about the keyblade you little piece of shit” Meanwhile overwhelmed by Sora being even shorter and somehow more impulsive than current Sora.
Meanwhile current Sora is just kind of like “oh huh that’s me” and keeps telling Riku to “give yourself a break, you’re just a kid haha!”
KH1-Riku being disgusted by how in love with Sora current-Riku is. Intimidated cause Sora is still just as cheerful but like /holy/ shit is that boy strong. KH1-Sora is just glad they’re friends again. Might start crying because of it.
But. /But./ My favorite thing to imagine is the look on KH-1 Riku’s face when he learns Sora has /two/ keyblades
i think one of my favorite bits of kh2 was right near the end, that realization that while sora, donald, and goofy have been adventuring around, riku & mickey have been doing the same thing? it just touched my heart. T__T ♥ it humanizes riku so much, even though their scene is so short.
au request batch 15! I HAVE A LOT TO DO NOW BECAUSE YOU GUYS ARE AWESOME AND I THANK YOU FOR THAT. i laughed and i died drawing this batch, ITS A MIX OF JOY AND ANGST GHHG (why does the worst one have to be the first on the liiiissssttt ughgh)
Edit: Since it’s come up a few times now: I don’t think Terra did anything wrong either. It’s probably a poor choice of words in the heat of the moment when somebody said “there is no changing back” for Terra and I was a little ticked off by it. I can however imagine that Terra himself views returning to the light and helping defeat Xehanort as redeeming himself.