It turns out that Square Enix originally suggested Mickey Mouse as main protagonist, while Disney on the other hand had hoped for the slightly quackers Donald Duck to take centre stage. Nomura wanted neither, and so the multiple-character setup was born.
As with any great RPG, there needed to be a signature weapon of course, and the Keyblade wasn't it..initially. What Nomura showed Disney and Square Enix executives was slightly...different from the family brand's image: A Chainsaw.
"Everyone got this scrunched-up look on their face and nobody said a word in the entire room. Dead silence. And I thought 'No, I guess this wouldn't work, huh?'- Tetsuya Nomura
Thanks to Joystiq: [Interview]