I really enjoy this story even though it confuses me a great deal. The reason why I am confused has to do with pronouns. Who is the she in the first paragraph? Who is the he in the second paragraph? At a guess I would say it is respectively Selphie and Wakka, but that is merely my best guess. Using their proper names would clear up this confusion.
But on to what I loved about it. I adored the concept you've written about here. It takes place after KHII I am assuming and I like your idea for a new problem that springs up around Sora and Kairi and Riku. I really cannot see the three of them fitting so seamlessly back into ordinary life in a small town and I really find your idea that they would somehow still be forgotten here to be intriguing. Afer all, they never did visit their own world to resolve those roblems of memory there that occurred all over the rest of the worlds. Also, this could just hint at new problems and new enemies pitting themselves against the trio.
At any event you write the characters reactions to such a strange phenomenon well. I like the way that Selphie is so shocked that Sora knows her name and the way that Riku is mistaken for a girl and Wakka's lists of reasons why Riku cannot be the real Riku.
The way that Selphie seems to be regaining her memory at the end looks hopeful for Sora actually and his ability to be reintegrated into the world he has left for so long. I like the way the three friends have to rally together so closely in order to feel okay in this strange world that doesn't recognize all of them equally anymore. There's something very poignant about coming home as a hero who is not only not recognized for his great deeds which no one really knows about, but also not recognized at ALL.