i was thinking, maybe the 3 knights, shown in the secret ending, are like
sora, donald, and goofy,
the three knights are like sora, kairi, and riku.
if you think about it, they are sort of following hte same path. mickey,the king, sent sora donald and goofy on a quest, well not sora, but sora got swept into it because of hte kyblade, so maybe, another king sent the other 3 knights out on a mission to defeat the evil, the uem. not sure. just a theory