So... this AU kicks off properly at the end of 358/2 Days. It's basis, however, comes from a conversation midway through Days, between Riku and Namine about Sora's memories:
So the implication is Xion - and most likely Roxas - could survive, but Sora would remain asleep much, much longer than he does in canon. And that's where the AU starts.Naminé: They're escaping through Sora's Nobody into a third person--and now they're starting to become a part of her. Riku: You can't get the memories back out. Naminé: If they're still separate...then yes, I think so. (She looks at the sketchbook on the table of the picture of Axel, Roxas, and Xion) Naminé: But if they join with her memories, things get a lot more complicated. I would need to untangle her memory before I could finish Sora's... What was supposed to take months might take years. DiZ would be furious.
After a lot of debate, they come up with a possible solution: Namine would let them live and untangle their memories and Sora's. Meanwhile, Roxas and Xion would go on the run from the Organization, and not use their Keyblades unless absolutely necessary to protect themselves and/or the worlds, in order to delay the creation of Xemnas's Kingdom Hearts.
On Day 353, when Roxas asks Axel why he let Xion go, instead of brushing him off, Axel (reluctantly) explains what's going on (and also Roxas is probably a little bit calmer so he actually listens to what Axel is saying this time). Roxas by extension learns a lot of things - both about Xion and himself. He deserts and runs off to try and find her and see if there isn't some way to stop what's going and and see if there isn't a way he can keep her from being destroyed.
He finally catches up to her right around Day 356, when Xion is speaking to Namine, taking them both by surprise. He talks to them both, trying to convince them to see if there isn't another way to make sure that Xion survives (and because he's figured out that he's Sora's Nobody and realizes he has Sora's memories too, he's able to guess his own survival hangs in the balance too).
DiZ turns up as he does in canon to announce Axel's arrival, and is surprised to see both obstacles to Sora's awakening right there in front of him. He tries to order Namine to incapacitate at least one of them if not both (think how she smashed Riku Replica's heart in Chain of Memories), but when she refuses, Xion and Roxas grab her and all three flee the Old Mansion.
They run into Axel outside, who still does have orders to bring both back to the Organization. Except he knows as well as they that the Organization wants one of them dead, so when they explain that they might have a solution that would allow them both to live, Axel pulls a line like "Get out of here and I didn't see anything." They also ask him to come with him, but he brushes them off and insists they leave, so they reluctantly do so via the darkness corridors.
((There's only one issue in this whole segment, and that's the fact that Xion is still absorbing Roxas' powers/energy. I'll account for stopping it somehow - suffice to say it's not an issue in this AU, especially since Xion is not reprogrammed by Xemnas the way she is in canon))
They go on the run for a little while, until they finally run into Riku, where they explain the situation. Riku appears reluctant, but eventually agrees, owing to the fact that they all know Sora would not react well if he found out that two people essentially had to give up their existence just so he could wake up. Riku takes charge of Namine and goes to find King Mickey to confer with him. Xion and Roxas, meanwhile, continue their flight around the different worlds.
Time passes - it's assumed that Riku, Mickey and Namine are successfully able to (on the whole) circumnavigate DiZ, who may or may not still have control over the unconscious Sora, Donald and Goofy. Xion's existence is slowly strengthened by her own memories the longer she's alive, though Namine realizes she will still need at least some of Sora's memories to survive - so she sets about slowly replacing the memories of Kairi inside of her with Sora's memories from Castle Oblivion. Xion's default appearance changes ever so slightly - resembling Namine instead of Kairi, though there's little visual difference because Namine is Kairi's nobody anyway.
Things don't go completely smoothly though. Organization XIII notices - of course - how the progress on Kingdom Hearts suddenly grinds to a halt, at the same time they lose their two Keybearers. They quickly adopt two main goals:
- Recapture at least one of them. Capturing the second is optional - destroying them is considered preferable
- Manipulate the Heartless populations of the different worlds in order to force Xion and Roxas to use their Keyblades in order to protect those worlds from destruction
Then there's Axel - on the surface, he's back to the wildcard status he had in Chain of Memories, seeming to antagonize Roxas and Xion many of the times he meets them, much to their dismay and confusion. Yet this is more for appearances than anything - what he's actually doing is subtly sabotaging the Organization's efforts to locate and capture them, while maintaining the illusion of loyalty. This doesn't last forever - Saix in particular suspects that Axel isn't actually trying as hard to actually capture his "former friends" as he could be, among other things. Once he's found out, he flees the World that Never Was and... I haven't decided yet. He could try to help Xion and Roxas similar to the way Riku did in KHII, or he might try to meet up with them and explain.
I takes roughly two years after the end of Days for Sora to actually, fully awaken. At that point, things have actually gotten pretty bad. The Organization is aware how much of a threat four Keybearers (possibly six if Riku transitions to Way to Dawn and Kairi gets Destiny's Embrace) would be to them, even if it did mean a resulting spike in heart collection. All sides are getting desperate (though by this point DiZ has given up on being a nuisance and retreated to try to come up with another plan, possibly even joining with Mickey and revealing his identity and handing over control of Sora, Donald, and Goofy). The Organization is stirring up as much trouble in the worlds as they can to force Roxas and Xion to use their Keyblades and collect hearts, and on the whole they're succeeding.
Kingdom Hearts is completed on the same day that Sora wakes up.
... and that's all I have so far.
[EDIT] Additional Notes:
- Riku is tentatively set to be not Ansem-ified by the time KH2 begins, because the fight with Roxas never happens. This is subject to change though, given that a lot of things could happen in two years and he might find himself forced to call upon the darkness if things get dire - which they might
- Kairi will likely get involved - most likely because she'll get tired of waiting and try to go to look for Sora the way she does in KH2. Organization XIII may get opportunistic about this.
- They may also find her letter to Sora, and use it as evidence that they holding Kairi (like they did in KH2), in order to bait the Days Trio - with Riku in tow - back to the World that Never Was as part of a trap, even if they don't actually have Kairi there; They'd know it's a trap likely, but it'd be a case of both sides trying to outwit each other.
- After Sora wakes up, assuming DiZ does give up and reveal himself, Namine will be able to actually be there when Sora wakes up, and will therefore be able to explain some of what went on. Riku will also be a little bit less set on avoiding him (unless he is Ansemified) and they might very well end up working together (again, if Riku is not Ansemified). This would partially be because Kairi has had some time to work on him.
- Additionally, after Sora wakes up, Roxas and Xion sort of... take on the role that Riku does in KH2 - fighting the Organization and helping Sora sometimes, but keeping themselves hidden from him a lot of the time (this is due to nervousness at how he will react and guilt about how he was kept asleep for so long - mostly on Xion's part). Riku and Kairi and the others don't tell Sora who or what they are - besides the fact that they're allies - because that's something they know Roxas and Xion will need to do, eventually. Axel may or may not act as liason when they really need to pass along information (Depends if they ever NEED one, besides they do have black coats too). As with Riku, they finally do meet up properly at the World that Never Was
- Possible (Probable) revision of Axel's role: He stays behind at the Organization, but more to play double-agent for as long as possible, and also to try to figure out if there's a way to keep Xion from destabilizing again and absorbing memories again, since Namine's patch is not going to be permanent.
- Possible (Probable) solution to Xion's absorbing problem: DiZ after a year-year and three months, concedes that his plan is not going to work anymore and turns over control of Sora, Donald and Goofy to Mickey, Riku and Namine, possibly revealing himself as Ansem the Wise in the process. Motivation is to still have some sort of hand in Organization XIII's downfall. Around this time, Namine's "patch" (which already lasted much longer than expected) starts to fall apart and Xion begins to absorb memories again. Realizing DiZ may have the knowledge and ability to reprogram her successfully so that she's stable, they ask him, but he refuses, maintaining his nobody/replica grudge (not to mention he probably considered the research/experiments that had made Xion the kinds of things better off left forbidden and untouched). It takes 2-3 months of Riku, Mickey and Kairi working on DiZ in turns - as well as him actually getting to see the Days Trio interacting during those times they come to Disney Castle - before he finally relents and reprograms her. Note that none of the Days Trio are thrilled at the prospect (none of them really trust DiZ), but they really have no other options - the only other person with the right knowledge and expertise to reprogram Xion is Xemnas.
- Sora takes a while longer to adjust after waking up then he does in canon - there's a whole lot more in the way of limbs to get used to. Riku is still probably taller though.
- Possible idea for an early part of the endgame of KH2 equivalent (How Sora finally meets Xion and Roxas): Xemnas attempts to capture Xion and reprogram her again, to try to force her into her bossform from the end of Days, as well as make her lose her mind/go berserk like he tried to do in canon. The idea is to try to start pitting Keybearers against each other, to narrow down the number of threats to the Organization. Additionally, Xion makes an ideal weapon for him against Sora, Roxas, Riku, Axel and possibly Kairi, given that none of them will want to fight Xion. The plan goes awry, though (possibly DiZ anticipating Xemnas's actions and putting some kind of hidden failsafe in there to keep her programming from being meddled with by anybody but himself/someone he's trained to work around the failsafe?)