This article is about No. XIV in the Organization
You may be looking for Sora.
Hayden Panettiere (BBS, KH3D)
"Never forget. That's the truth."
Xion is a puppet created by Vexen as part of the Replica Program for Organization XIII. She's designed to duplicate Sora through his memories within Roxas, and thus is able to wield a Keyblade.
After her death in Kingdom Hearts 358/2 Days, anyone with memories of her forgot her existence until Organization XIII used her as the 13th Darkness for the battle at the Keyblade Graveyard. After failing to end Lea, she aligns with the Guardians of Light, betraying Organization XIII. She then helps Sora and Roxas fight Saïx after Kairi was abducted by Xemnas.