AN: Just an attempt to explain Riku's rather miraculous recovery in the ending movie, where he goes from being unable to walk to walking, swimming, swinging Mickey around…
Oh, the Flare thing? Pet theory. Riku's power is supposed to be Darkness and Light, but we don't see much of his 'Light' powers beyond his Keyblade (which, granted, seems to be all there is to it, but…). But twice in the game, we get scenes where the screen goes white, and then a crowd of enemies disappear. The first is when Kairi gets pinned, so I assume it was something Riku did. Then we get it again at the very end against the swarm of Dusks. Less evidence there (it could very well be just a 'curtain drop' sort of thing), but Riku does seem to come out the worse from that fight, despite the fact that he was kicking ass beforehand. Which means either he's been healing Sora up and Sora has been neglecting to heal him, or he just got hit with something massive.
As for the side-effects – particularly, not being able to use magic – well, that's my way of explaining A: why he didn't seem to be using his powers in the cinematics while he was still in Ansem form (despite the fact that he'd chosen said form for the way it allowed him to use the Darkness), and why he didn't just slap a cure on himself after the final battle. Yeah, yeah, I know – it's Sora's show, the Storyboard Demands… but we still need a logical in-story explanation for why.
The dark shore was quiet – only the faint whisper of wind, the susurration of the waves on the sand, and the ringing in his ears. Riku winced inwardly and wished his body would ache a little more quietly. That last battle had cost him a lot more than he'd anticipated, particularly reaching through his sometimes patchy connection to the Light in order to cast that last Flare and deal with the horde of Dusks. It wasn't just the sheer drain on his body or the fact that it crippled his ability to use magic for a relatively long time afterward. The damn thing had pulled energy from previously cast spells as well.
Which meant that not only was he feeling the effects of fighting the Dusks and soaking several massive hits from Xemnas to buy time for Sora to get that last attack in, but he was also feeling the half-healed damage from wounds he'd slapped a quick healing spell on in the middle of a fight.
Long story short? He hurt. Everything ached – well, except his left leg, where he'd gotten slammed into a flying skyscraper. (The hell? Buildings as projectile weapons? He'd seen a lot of crazy stuff over the past year and a half or so, but sometimes you had to draw the line!) Unfortunately, that was because he could barely feel his leg at all. He suspected the impact had broken a bone, and he'd slapped a Curaga on it so fast that he just hadn't noticed. Which was nice for killing the pain and keeping his leg from collapsing under him – not so good for making sure he didn't accidentally make the wound worse if he didn't give the spell time to work.
Then the Curaga spell was drained away by that Flare, and now his leg wasn't working at all. Great.
Granted, it wasn't like there was anywhere to go.
Sora was doing his best to be subtle about the concerned glances he kept shooting Riku's way. Sora being Sora, that only served to make them more blatant. If Riku weren't so tired or just didn't hurt so much, he'd smack the dolt. But moving involved far too much effort and pain at the moment.
"Oh!" Sora yelled.
Riku jumped to his feet. At least, his reflexes tried to do so. The motion was aborted rather completely by the fact that his left leg didn't respond at all and the rest of him ganged up on his pain sensors for the ludicrous idea. Sucking air through clenched teeth – like hell he was going to whimper like Pluto did when nobody played with him – he waited for his vision to clear and looked up at Sora. "What?" he snapped. He didn't mean for it to come out quite so sharp – but he'd forgotten how noisy Sora could be sometimes.
Sora was rummaging frantically through his massive pockets. "I have Potions! And Hi-Potions! And Elixirs! And… wait!" He stopped. "Why am I bothering with that? I can cast Cura…gah."
Riku's fingers twitched around Sora's throat. His arm was screaming in pain, but apparently irritation was a stronger goad than alarm. "Why," he asked flatly, "didn't you mention that before?"
"Um… I forgot? Eep!" Before Riku's hand could do more than spasm, Sora hastily called, "Heal!"
Green light washed over him; Riku's eyes slid closed of their own volition. He didn't exactly let go of Sora – it was just that his bones and muscles all seemed to melt in the wake of the sheer, overwhelming sensation of not hurting.
After a long minute, Riku's eyes opened slightly. Sora was still looking at him. Weird grin on his face, though.
Fortunately, recovery meant that his response time was back to where it was supposed to be. Action was simultaneous with thought.
"Owww!" Sora pouted, rubbing the back of his head. "What was that for?"
Riku just smirked and relaxed back again to continue enjoying the absence of pain. "Idiot."