The mirror is pristine, a simple sheet of glass set into the wall. The mirror tells no lies and speaks only truths.
Xion knows this, and so Xion likes the mirror.
She looks at the girl reflected in it, and knows that she will become something. The mirror assures her, she thinks, and it tells her that one day, she will mean something; she, and the blonde-haired boy, and his tall red-headed friend.
When she meets the silver-haired boy, she wonders why he wears the blindfold. Maybe he doesn't want to look in the mirror, or to hear what it says to him.
When Xion sits at the top of the tower, on the precarious ledge, and watches the ground sway beneath her and feels the soft summer air caress her face, she knows that this is real and one day she will be real.
When she feels the warm weight of the Keyblade as it coalesces in her hand, she knows that she has purpose; she has a destiny.
But one day, Xion wakes up and does not see herself in the mirror. She sees a boy with brunette hair and cerulean eyes that are not hers but at the same time are, and No, no, this isn't me, I don't want to be this…
Because now she knows that she cannot become something.
She breaks the mirror, flesh connecting with glass, and it shatters and falls to pieces at her feet in fragments – that's all I am, a fragment…that's all I'll ever be – and blood that isn't there falls in rivulets as she collapses.
No, no, I can't be this, I can't be a tool, please no…
But deep down, Xion knows it to be true - because the mirror told her so, and the mirror does not lie.