Mickey figured Oz would have questions, since things were much different now than they were back then. "Nobodies are the shells left behind when a person with a strong will becomes a Heartless. It is believed that they are not supposed to exist and have no real emotions, since they don't have hearts". The first question was hard for anyone to answer. As for the second, it was alot easier to answer. 

"As for Sora... he was a Keyblader from about two hundred years ago. A boy who saved the worlds from the Heartless and Nobodies before, having foiled the plans of Maleficent in his first journey and Organization XIII, a group of powerful nobodies, in his second journey. He made many friends on his journey..." The King paused for a moment, a slightly somber expression upon his face. "He is gone now, and has been for a long time. Regardless, he was a very dear friend of mine, Donald's, and Goofy's". 

To change the mood from its current somber shift, Mickey returned the topic to the matter at hand. "Anyway, do you have anymore questions? If not, you should probably get some rest before the others get here. While I hope the investigation turns up nothing serious... we should probably be as prepared as we can".