The first part of the theory was how Namine and Roxas were made.
Which has been stated nicely but let's hear you our regardless.
Kairi couldn't make a heartless so her heart left her body.
Actually, her Heart leaving her Body at all is a mystery. The Heart leaves the Body when? When it becomes a Heartless. Why then would Kairi's Heart, belonging to a PoH, leave its body at all? Mystery.
This isn't how Xion came to be because nothing happened to Kairi's body either.
I like it when people say this. It's easier for me to raise a possible counter argument against it.
Namine came from Sora yet Sora's Body and Soul were Roxas. What is Namine made of then? Possibly the same thing as Xion that lets her "be" despite the fact Kairi's B+S are still in-tact.
Her heart went to the person that had a pure heart
Sora? Pure Heart? What did I miss?
It couldn't be Riku because his heart was full of darkness
How about the fact he wasn't even there? XD
When Sora stabbed himself(emo)
Because there's nothing more emo than sacrificing yourself for the greater good and saving your friends.
/Sarcasm
his and Kairi's heart came out his heart helped him form a heartless
You mean his and Kairi's Hearts leaving Sora's
Body made for Kairi to wake up and for Sora to turn into a Heartless.
I guess Kairi's soul was with her heart
If her Soul was with her Heart, her Body would've died. Body - Soul = Death. So no, her Soul never left her Body, only her Heart did.
and it somehow fused part of itself to Sora's body and made Namine.
Which would then require an explanation as to how Roxas is an incomplete Body. Which hasn't even been hinted towards, since AtW constantly repeated in his Reports how Namine was made of all but Nothing incarnate.
So what about Xion's connection to Sora's memories?
What connection to his Memories? The "she can't endure it"? Take it as Namine talking about Kairi and move on with your life, it makes much more sense that way.
Since there were 2 hearts in Sora they made there own nobodies but also there own combined nobody. Xion, the combination of Sora and Kairi.
The combination of Sora and Kairi is Namine. Kairi's Nobody, who came from Sora, and has ties to Sora's Memories and Heart.
Thats an even weirder existence than Roxas and Namine's.
You're under the painfully mistaken assumption that Roxas and Namine's existence are of a similar nature. They're obviously not.
This is probably not right but its a theory I just thought up. Again please don't flame.
Not flaming, just amused somewhat. Nice try though.
Maybe Sora and Kairi hearts combined to make a whole new set of memories and maybe even a new heart (but that is similar to what bladewarrior 13 said) anyway for all we know Xion could have memories of both Sora and Kairi( somebody tell me if Im wrong about Xion having both Sora and Kairis Memories)
Xion has no Memories at all. Hearts don't just 'give birth' to another Heart or another Memory. Things don't just appear out of nowhere.