Sora is stuck inside his Happy!Egg, while Naminé looks after him. She tells Riku that, despite the fact that Sora is perfectly healthy, he cannot wake up because something is missing.

A short time later (a few days, maybe a week), Riku finds himself battling a Keyblade-wielder in a cloak not unlike his own. After winning, he kneels down to get a better view of his opponent, and is shocked by what he sees and feels. This is Sora. Not physically, for this is a girl, but somehow she is Sora. The mysterious figure takes Riku’s shock as an opportunity for one last attack, but is foiled. Riku begins to walk away.

“Why don’t you kill me? You won the fight, now you can’t finish it?”

Riku explains the connection that he felt, and explains that he could not possibly kill a manifestation of his friend. The cloaked girl cries out and collapses, and Riku leaves.

Organization members find the girl, known as Xion, and bring her back with them to become their newest member. She quickly forms a strong bond with Roxas, and cannot help feeling connected to him in some way. Roxas, accidentally and unknowingly, allows Xion to replace his best friend Axel. After some time and due to the deep connection she feels with Roxas, Xion begins to suspect that there is some truth to what Riku said. She explains this to Roxas, who suggests that they find Riku and confront him about it.

As soon as they fill him in, Riku can tell that they’re right. These two are the missing parts of his best friend. They will complete him. Riku can feel Sora getting stronger, but he watches as Xion and Roxas begin to weaken. Xion collapses entirely, and Riku stays behind to look after her while Roxas goes back to tell the Organization that they will be losing their two youngest members.

Axel is shocked. “You think they’re just going to let you walk away?”

“They won’t find us.”

Axel follows Roxas to Twilight Town, and watches as he meets up with Xion, who has grown even weaker and more dejected. Not wanting to hurt Roxas, and knowing that Xion will make for an easier fight, he engages her in battle.

“You two can either come back with me now, or they’ll find you and destroy you.”

Despite her condition, Xion fights Axel, using up every bit of strength she has. Roxas cannot allow his two best friends to kill each other like this.

“Stop!”

Xion is momentarily distracted, and Axel takes this opportunity to deliver the final blow. Realizing what he’s done, he flees, not willing to face his friend.

Roxas catches Xion as she staggers and falls. Before her essence turns to light and shatters, returning to its rightful owner, she tells Roxas that he has to find Sora. Together, they will complete him.

Furious, Roxas travels to The World That Never Was to find Riku. “She died because of you and your stupid friend! She’s gone!”

Riku allows his darkness to dome forth from his heart and is able to overpower Roxas. Riku takes his captive to Naminé, knowing that his job is finished.

Naminé nods. “Wake up, Sora.”

“Now, one must ask, what if there had been no Xion? What if Roxas had never known about Sora? Would the master of the Keyblade still have been saved? Would his soul have been repaired? Of course. That’s the inevitability of it all.”