Okay, so I'm still fine-tuning my ideas. But, in the meantime, I'll share what I have in mind thus far to make sure it's kosher:

I have a group of youngsters who will be involved in fighting Heartless, one way or another. However, the group ends up being scattered across the different settings. So, my character's goal is to locate those friends of his. I know I want my character to be a keyblade wielder, and possibly one of the others. But, I'm not sure about the rest of them.