As potentially a Sephiroth fight replacement.

 

Meet the Mayor of Destiny Islands and adoptive father of Kairi:

 

Well my initial thought was that, first of all, Kairi would only be his adopted daughter, plus the whole mayor thing could fit in with the maester thing.

 

Actually, he may be better as like the son of someone in the Islands. Seymour could then try to pursue Kairi like he did Yuna

No, no and again... no.

I'm sorry.That makes about as much sense as Cloud being Sora's father

What about Kairi's actual parents? what if she has one final fantasy parent and one KH original parent?

Sure. And let's put Batman in kh3 along with him.

I can't see it happening. 

I prefer Lightning.