So, I saw this thread, and it got me thinking about this topic. Riku, Vanitas, and Xehanort all use the same stance. In Vanitas's case the reason is obvious: He was trained by Xehanort.

But then there's Riku. We see that he uses that same long before coming in contact with Xehanort. Specifically, Re:CoM shows Riku using that stance when he was a kid.
So, what could be the connection between Riku and Xehanort that makes them choose the same stance? After thinking for a bit, I came to a conclusion. First, what do Riku and Xehanort have in common? They are both from Destiny Islands. So what about their battle stance? Simple: That is a traditional swordman stance from Destiny Islands. Not everyone uses it, as seen by Sora, but the stance comes from there.

So, what do you think?

I mean, I guess that's one way to look at it, or it could also just be a cleaver nod to the fact that Xehanort would end up possessing him one day. But since I doubt they're ever going elaborate on that, this would be some decent headcanon.

That makes sense,but I doubt Square Enix though about it this way.I think they are just reusing stuff like Riku and Vanitas having similar clothes.

Probably just something they created before making it relate to Xehanort, etc. in the future games.