Input (grade 12): Organization XIII controls the Nobodies, the bodies left over when a person with a strong heart is turned into a Heartless.
Output (grade 10): As they search for him, they meet the rest of the members of Organization XIII and learn that they are beings called Nobodies. When a Heartless steals someone's heart, that person also becomes a Heartless, but if their heart is strong, their body becomes a Nobody.