So just what is a keyblade anyway? It looks like a key but counts as a sword? Let me explain: The Keyblades are simply manifestations of the kingdoms's own hearts and powers. They are divided in 2 seperate categories, Kingdom Keys and Lesser Keys. The Kingdom Keys being a weapon which finds itself to the one of strongest heart, the kingdom itself having recognised them as their protectors. The Lesser Keys on the other hand are smaller manifestations of said power which exist as physical objects, while not being as picky as the Kingdom Keys they still bind to a master when wielded but once. As for what their strange shape and actual purpose are....
only time will tell
only time will tell