i have played the first kingdom hearts quite a few times and i believe that on releaseing all three hearts within sora (kairi, ventus, and his own) that kairi then took all three hearts and gave sora his back (this is all speculation) but after the moment when sora got the keyblade back in the first kingdom hearts (when riku took it from him and then said "my freinds are my power" which is also a ventus quote) he obtained the ability to use the keybloade just with his own heart, that's why when kairi gave his heart back (once he'd become a heartless and then they did the whole cuddling thing and he came back) he could still use the keyblade and kairi is now storing both her own and ventuses heart within her, she also was accidentally given the power to wield a keyblade by aqua in bbs, not to mention she's a princess of heart (or whatever it is) so i'm thinking that kairi could have an extremely large part of story for kh3!!!!!
