This time, I'll protect you.

General concept: a Kingdom Hearts AU where Kairi wasn't able to restore Sora to his proper form during Hollow Bastion, and has to figure out a way to take up the Keyblade and help defeat Ansem in his stead (while Sora has to figure out a way to help as a little scrunkly guy).

Major changes:
★Kairi has to take up the role of the "Keyblade master" in the Sora-Donald-Goofy trio, though she doesn't immediately have access to said weapon.
★★Organization XIII probably wants to control her, instead, for this key (even though it's still technically tied to Sora's heart).
★★Being a Princess of Heart as well, a lot of stuff just doesn't affect her as much and she can do some special things too. (Trying to keep that mostly to canon possibilities rather than make stuff up.)
★Sora is a Shadow Heartless who retains his will thanks to Kairi. With his body gone, he's too small and weakened to use the Keyblade, and he can't speak.

(Two months later edit: amusingly, the hardest part really might be figuring out how Ansem is dealt with. Probably a lot of the power of friendship and love, sure, KH1 was in a very earnest and simple place -- but it still needs to be narratively satisfying.)

Sora is so important to the plots that this causes a lot of crazy shit to change, frankly. Let's go over what *doesn't* change:
★★Ventus's heart is still in Sora's. This means his little Heartless form...isn't, technically.
★★Roxas is still created and recruited by the Organization. He still looks like Ventus.
★★Naminé is also created and also still resembles Kairi. Because she has power over Sora and his closest friends, Kairi's memories of Sora can be changed, too, so Chain of Memories happens but he isn't targeted.

And everything that does:
★★Sora and Kairi don't part. For those in the know, he stays nearby as a Shadow and does whatever he can to support them in combat and emotionally. For those not in the know, he literally hides in her shadow. And even Heartless don't realize he isn't one of them.
★★★Rather than a Keyblade wielder, he grows into an unusually strong and benevolent Heartless (sort of like a Neoshadow in abilities by the end), an agent of intrigue like Riku, and a source of morale. Unfortunately, being a Heartless isn't good for you, even with the support of a princess of light — he forgets many things about his human life (including the ability to write), just never his friends. And the worse things get before his recompletion, the more the darkness of his heart might grow...
★★The Organization isn't aware that Sora is still "alive", let alone that the Keyblade is still tied to his heart. They assume Roxas and Kairi are their only ways to get the power of the Keyblade.
★★Xion is generated by Kairi's leaked memories, and as a result resembles the person she most recently "lost" and cherishes most: young human Sora...maybe with some Shadowy elements. Or maybe Riku, since Sora is still unknowingly with her? Xion's gender will probably be male or NB, but more importantly, being an artificial Nobody of *Kairi* means Xion can't natively use the Keyblade, not even Roxas's. The Organization deems the project a failure and they're never really introduced as a member...which doesn't mean they don't play a part. Kairi's recovery still comes to a standstill with them alive, and they might not appreciate this excuse for a life if they learn...Sora might even be the one to find them.
★★It's entirely possible that Roxas never defects. His existence weakening Sora's recovery doesn't come to matter with Sora awake and unmodified but a Shadow, and the failure of No. i and controlling Kairi causes the Organization to have to treat him *slightly* better as their single resource for the artificial Kingdom Hearts. He doesn't impede Kairi's recovery, and only really has Axel and maybe Demyx as friends. Riku still eventually learns of his existence and maybe even seeks to bring him down in hopes of recovering Sora, but Sora himself learning that Roxas is an entirely different (and still sort of benevolent) person might be enough to cause him to convince Riku to let him be, at great personal sacrifice, and instead try to convince Roxas to defect for its own sake. In any case, he never needs to be captured and put in the simulation. Kingdom Hearts II goes very differently with him still around throughout it...who knows what would happen when he meets the literal heart of his Somebody?
★★Because Axel's relationship with Roxas doesn't fragment, he's playing a less desperate role in II, as well...though possibly still trying to convince Roxas to stay in the Organization for his safety (and Axel's own comfort).
★★Kairi never reaches Destiny Islands again until the end of II. She also doesn't randomly get her own Keyblade from Riku — it remains Sora's and requires him in the same general area for her to summon, using the link to his heart.
★★Speaking of Riku, he never unleashes the full depths of his darkness to defeat Roxas, though he might do so against another mighty opponent in II...the whole "looking like Ansem" subplot isn't as much of a thing, anyway, since his friend is literally a Shadow and Kairi is always there to help. But more importantly, he also *struggles* more with his darkness without that outlet, to the point that he continues having to rely on Soul Eater.
★★Data-Sora's heartless is taken over by the real Sora and helps eject Pete and Maleficent from the datascape. Not for any real reason, I just think it'd be cute and/or funny.
★★★Wait would this be the part where they realize that Shadow Sora could maybe use technology to communicate normally or something?? Oh god Re:coded relevance strikes again
★★Riku is the one targeted to become a vessel by the Real Organization in the trials of DDD. Being Kairi's Dream Eater and not the other way around, this almost goes *better* for them just because it's harder to reach him...if not for the existence of other helpful characters, including Sora.
★★Kairi slowly loses access to Sora's Keyblade throughout DDD and has to fear for her life, mostly alone, relying on magic as the beginnings of the Real Organization simply do their best to kill her so that less capable Princesses of Light can spring up and be their targets for the artificial Keyblade War.
★★Near the end of DDD, both Riku and Kairi, and other supporting characters, suddenly generate their *own* Keyblades. This is partly due to proving strength of heart, and partly due to Master Xehanort's time-travel trick causing Kingdom Hearts/Master of Masters' malevolent light to start spewing light Keyblades in recognition of another "Keyblade war".
★★With Even's defection as a "backup" member of the Real Organization, they realize they can recover Sora while keeping Roxas alive. Roxas "unlocks" his heart (soft-suicide in a mirror of Sora's KH1 sacrifice, his "last words" are Here Goes Nothing because it's a nice sad pun) and remains in the replica while Sora allows himself to be slain by the Keyblade and is finally recompleted...somewhere else, to their horror. Part of III on Kairi's side is spent looking for traces of him in Disney worlds (while, mostly, rebuffing the Organization's attempts to kidnap Princesses of Light), and the worlds of the Realm Of Twilight, after a search of Radiant Garden turns up empty — though he's actually stuck in the Realm of Darkness due to the part of Hollow Bastion where he was split in two having been long lost to it, as well as the immense strain on his original body from Roxas and his heartless being around for so long. Thankfully, he retains his Keyblade, if not necessarily his cheery disposition and a large chunk of his memories, and he quickly develops the ability to enter Anti/Rage Form naturally as a result of his long, long period as a Heartless. (Unexpectedly, he can also sometimes channel the sort of pure and immensely powerful light that Kairi had sustained him for so long with. In that sense he becomes the yin-yang bomb Roxas is known as in the canon, while the latter really is "what if Sora was trained as an Organization member instead of through experience" because he never faced the powerful grief of losing Xion.)
★★Sora encounters Aqua and Ansem within the Realm of Darkness before Riku and King Mickey even find him. (He can commiserate with Aqua being separated from her natural place and state for so long that even the world and "destiny" seems to want to tear her apart.) But he can't naturally find his way back to the light like he could in II, and he isn't strong enough so soon after a traumatic recompletion to prevent Ansem from being taken away, even with Anti/Rage. Aqua, however, is, her own connection with Sora allowing her to briefly use his Keyblade too. Still stuck within the Realm of Darkness, the three team up to search for a way out with renewed vigor and the help of the Keyblade.
★★Without proximity and Kairi keeping Sora's heart together, Ventus's heart slips free as it travels and he reawakens in Castle Oblivion, perhaps even re-experiencing parts of BBS as he wanders (I'd like to speculate about weird stuff regarding his and Terra's Keyblades appearing to Aqua, and the nature of the Keyblade Graveyard, at this time — but how the time of BBS worked is something that might be better kept vague). Vanitas might find him early, and...that might cause bad things to happen, or maybe prove that despite his long sleep he's still strong enough to overcome Vanitas. (A little bone for the Ventus fans.)
★★Final lineup of seven: Kairi, Riku, Sora, Mickey, Aqua, Ventus, Roxas. And Donald and Goofy are there too. (Axel *might* be there? Being the funnyman?) It's kind of weird and stupid that the thirteen have several who *don't* wield Keyblades given the whole "artificial Keyblade War" thing, so the "ancient keyblade wielders" on the team occasionally use dark copies of No Name, much like Kingdom Key being shared so much up until now. Most importantly, Xion isn't on the team because they never possessed a Keyblade...Roxas is. (Unless Xion's copy abilities are useful enough and/or two of Roxas's heart from different points in time can't coexist, which is probably the case actually, nevermind.)
★★Believing Sora comparatively insignificant and the 7 lights relatively measly in comparison to most of his team, Xehanort's plans for the final battle don't hinge on breaking him, but instead on trapping and distracting their most powerful members: Mickey, Aqua, Kairi and Riku. He simultaneously over- and under-estimates the team and has convoluted plans on plans to adjust to any foreseen issue, of course. He might even *fight* their attempts to use him as a portal with the formidable power of the X-Blade.
★★★Ultimately his failure may stem from his traditionalism, given the extremely unusual circumstances of many of the 7 lights due to their strong bonds of friendship and love. He's also a friendless dork so that definitely hurts his case.
★★Though not falling as pathetically as in III proper, there are still *immensely* strong villains and forces on Xehanort's side, and their plan *is* to kill the 7 lights so they can instead safely use the new princesses of heart to forge the X-Blade instead. So they will probably, again, all die and end up in the Final World, though Kairi is possibly the strongest princess of heart ever by this point so she manages to keep Sora *and* Riku together. Perhaps just as well, since there may be more than the Lich awaiting them...
★★Speaking of the cursed plot of III, aside from finding Sora and Aqua, Naminé takes Roxas's place as a lost heart whose absence is regretted, and due to slipping free on his own, Ventus doesn't necessarily need to be rescued. Still, the power of waking is recommended to be found by someone...probably Riku. He was Kairi's Dream Eater, after all.
★★★Naminé still has her powers of being linked to Sora's memory, which allows her to begin regular healing sessions with him once he's returned (because rather than his chain of memories being broken, many pieces simply remain swallowed by the darkness), and also allows her to eventually sense, seek out, and call to a tortured spirit who also remembers Sora: the Lingering Will.
★★Oh yeah, spoilsies: as a last resort when his pool of capable keyblade wielders has run dry, there are no viable possession targets, and the 7 lights are threatening to simply *magic* him into submission rather than clash with keyblades for his final piece — Xehanort divides them again, manages to subdue Sora and freeze him, and then shatters him when Riku comes near, causing sufficient grief and rage to override his reason and lead him to attack, summoning the X-Blade.
★★★So yes, Sora is saved by Riku using the Power of Waking, and post-III plot centers on trying to find and save Riku in turn. I'm trying to maintain a balance of narrative importance here. :b Kairi is by this point the main "exploration hero" and a princess of light, Sora had a bunch of crazy stuff happen to him and is the heart and soul of nearly every endeavor, and Riku was the villain of 1, an agent of espionage, the "victim" and protagonist of DDD...but not much more than that. He's the lancer. So he performs this huge sacrifice, putting him in the spotlight for a time, and his individual bond with Sora gets to be explored too. Donald, Goofy, Roxas, Ventus and Aqua remain more supporting characters in this context, I think. (Axel and Terra, when/if they are elements, doubly so.)
★★★Speaking of bonds, uh, I think the three of them might all be bi and in a polycule but I wouldn't want to *say* that out loud
★★And then IV happens with Riku in Quadratum and we have no idea what happens in IV yet. Woo! By the time I've even *begun* writing all of this it'll be out already, though.