[quote=@WanderingDragon]
Okay, so I just happened to have (mostly) finished a character who'd fit right into this. [@Double], you might recognize him.

I have a question, though; So we're not going off KH's canon, but is there any possibility such characters could appear in this plot?
[/quote]

Most Canon KH Characters have an Original Character Counterpart, sadly. 

That said, people who come from legit Alternate Histories like Big Hero 6 and Final Fantasy: The Spirits Within + Final Fantasy Unlimited (eww!) might appear.