Having survived his encounter with Sora, Xaldin traverses the Sea of Stars creating more Heartless and slaying them, in the hopes that he can one day regain his heart. It brings up events prior to ...
He'd been an apprentice under Ansem the Wise, the ex-ruler of Radiant Garden. During that time he learned many a thing from his so called mentor, and yet at the same time, he was perhaps little more than a guard, who was to keep intruders from entering his precious castle. He never thought that his dear apprentices would turn on him, and cast him into the Realm of Darkness. Their master had been a fool. Darkness was a powerful thing, and its lure was not an easy thing to resist. After casting their old master aside, his former apprentices, now Nobodies formed the first six of Organization XIII. Their ultimate goal, at least according to Xemnas, was to reclaim their lost hearts. And Xaldin's main role within the Organization was to create new Heartless, and in turn new Nobodies, which could help create the one thing they needed to achieve their goal, Kingdom Hearts.
During his time within the Organization he had traveled to many worlds, slain many Heartless, and turned many of those with hearts into Heartless. He did so using perhaps his most powerful weapon. He played off the fears of those he turned, he made them frightened of what was to come. This fear would turn to rage, and that rage would consume them, turning them into nothing more than pests who constantly sought hearts. They in turn would create more Heartless, and once there were enough, Xaldin would slay them all, as he had always done.
But those were days long passed, the Organization was no more. As far as he knew, he was the only one who had escaped with his life. He doubted that certain others would have been defeated so easily, but until he had some sort of contact with them, he would assume they had not made it. And that was an assumption he was fine with, for it meant he had no obligations to those who were too weak to live, he was no man's dog. He was now his own master. The only voice he listened to was that of the wind's, and it ruled him not. Which is why he was where he was now.
He had made his way across the Sea of Stars to a world where the inhabitants knew not of Nobodies, and after seeing his display of power, after seeing him turn others into Heartless, they believed him to be a god. They called him the commander of the wind, the king of battle, and the judger of souls. Normally he would have dismissed them as nothing more than ignorant peons to be turned and slaughtered, but this was not a chance one had but once in a lifetime. So he decided to make the best of it. This "god" was going to use his "divine judgement" to condemn this world's inhabitants, and turn them into Heartless. He was no fool though, he had heard myths and legends of gods that had been bested by mere mortals when they grew tired of the way they treated the humans, and Xaldin was no god. But with the wind as his ally, he would not be taken by any normal person. He would stay and continue his mission until the wind howled its warning to him. And at that time, he would take his leave. But for now he would be a god.