"You don't exist." Well, that explains... why he can't remember her. Or couldn't, because his memories are rearranging themselves even as they're talking.

He shakes his head, half-wanting to step forward and hold her but then he realizes it's because he can't help but see her the way he sees Kairi or Sora. So instead he stays in place, but he reaches forward anyway, trying to... he doesn't know what he's trying to do. What he does do is put his hand on her linked ones, trying to ease them apart gently.

After a moment, he speaks again. "Just.... you're doing fine. There isn't one way to go about this. And it's... a unique situation." Even when Roxas went back to Sora, he still existed. Riku never forgot, just like Axel never forgot, or Sora never forgot. So why... did they forget Xion?