Sora's mind was a variety of stain glass platforms connected by blue glass stairs. It was gaining pieces back, and Xion understood why she had 'shattered'. She'd been made from these glass memories, or shards of them. So she returned to them. None the less she was endlessly lonely for a few weeks, though at times the empty halls felt oddly familiar. Then a tug of familiarity struck her while she walked over the shard that showed Kairi sitting on the docks. Xion spent much time there, always wondering why she resembled her in her truest form-through Roxas's eyes.
The tug grew stronger as time passed and more glass platforms appeared. She turned at last and saw why. On the platform not far from hers, standing as if in Sora's shadow in that glass image of the Keyblader, was Roxas.
"Roxas!" Her feet carried her and she ran down the blue stairs. He hadn't turned, but she suspected he simply couldn't hear her from the distance. All that she could think of was seeing him again, talking to him. Eternity, or however long she was trapped in Sora's mind, seemed all the better if he was there.
As if to kill the hope, it was as if an invisible wall stopped her at the base of the stairs. Xion could not pass it, and Roxas was just beyond it. She called for him again, banging on it, but it seemed he couldn't hear or see her. She was trapped behind a one sided window, screaming out in anguish as she banged her fists in a futile effort.
Time passed, and she felt Sora defeated the Organization. She was saddened to feel Demyx go, for her had never been mean to her. It was when Axel faded that pain struck.
Roxas had been sitting silently, immobile, since he'd arrived. But when Axel died he jerked his head up and screeched.
"No! You can't! You promised we'd meet in the next life!" Roxas was shouting, sobbing. Xion felt pain shake her, for Axel had tried to include her, tried to shelter her. On top of it all, Roxas was in pain over it. She wanted to reach out to him, to hold him like he held her, as he cried. Yet she couldn't, the accursed wall making her...nothing. All she could do was hold a hand to it and wish he could hear her, if nothing else, so she could comfort him. The anguish lessened as time passed. Xion felt a certain glee when Sora defeated Saix and Xigbar. Finally, the 'Kingdom Hearts' was broken. The 'ceiling' became a sky, filled with stars. The sound of water and wind filled Xion's ears as Roxas finally lifted his head.
"Roxas."
She was hopeful once more as he stood up and began walking toward the stairs. Xion rose, trembling, nor sure what to say. She soon learned she didn't need to. Roxas walked right past her, shivering a moment, and continuing up the stairs.
"Roxas...?"
Xion stated at her hands, and wondered if she were only ice crystals. Her attention was grabbed instead as she turned and there was what Roxas had sought to join. Namine had been on the stain glass with Kairi's visage. That's my platform! Perhaps it was the envy for the fact that Namine could hold Roxas when she couldn't. Which they did, as the glass faded away and became sand on a dark beach, the inverted Destiny Islands. Their embrace was the last thing Xion saw before falling into the Abyss of Sora's sealed memories.