not trying to look smarter than you
Good luck.
but wouldn't the keyblade kairi used, if it was riku's keyblade, return to riku immediately????
Deep Dive, Roxas letting Riku use the Oblivion for the duration of their battle against the Neo Shadows and then for their fight. Riku at that time had no Keyblade of his own - part of why Roxas even had to give him the Oblivion to use. Should the Wielder wish, the Keyblade could be used by someone else, it appears - yet the one sustaining it would be the Wielder, not the User, should we call it.
Oh and I just remembered - Sora using Riku's Way to Dawn. Mmhm.
remember when leon tried to swing the kk in KH1, it returned to sora without sora knowing. i mean, that kinda threw me off when you said that. could ya please clear it up?
1) With Leon it was an extreme since Sora had just gotten the Keyblade. Both Sora and the Keyblade were probably going on instinct then once Leon swung it around. Also, keep in mind the Keyblade seemed just fine being materialized yet away from Sora, indicating it could indeed remain present though away from its Master. Leon using it gave it a good enough of a reason to teleport back.
2) Second case in point would be Jack Sparrow in KH2, but that one was obviously intentional. Even if Sora didn't actively call it back and only went according to what happened in KH1 with Leon, fact remains that he did not wish for the Keyblade to remain with Jack, thus - it didn't.
Then we have the entire issue that neither Leon nor Jack could probably Wield, while Kairi had the entire PoH-thus-related-to-Keyblades thing going for her if not her getting something from her Heart being in such close proximity to Sora's for so long. Not saying she has her own Keyblade, but it makes much more sense that she'd be able to Use a Keyblade at all compared with other people - as long as Riku was willing.
As for us never seeing it returning to Riku, we've never even saw the Keyblade for more than 3 seconds. It obviously wasn't important enough to show where it went to.
Facts remain that it was Riku that gave it to Kairi, and the novels that explain where it popped up from to begin with, again - being Riku.