Nobody

A Nobody is a type of humanoid creature found in the Kingdom Hearts continuum. Nobodies are what is left behind when someone's heart is lost to the darkness: a body motivated by only a soul. The most notable Nobodies are the members of Organization XIII.

Humanoid and Semi-Humanoid
Most Nobodies are pale and twisted creatures that only barely qualify as being humanoid. Those that do resemble humans are quite rare; not counting the artifically created Replicas, only fourteen human-shaped Nobodies appear over the course of the Kingdom Hearts series.

The appearance of a Nobody is dictated by the amount of willpower an individual had when his or her heart (which, it should be noted, are not 'hearts' as understood by medical professionals﻿) was consumed by the Heartless. Those with very strong wills are able to retain their appearance of humanity. Because of this, the strength of any particular Nobody may be roughly determined by how human they appear. Humanoid Nobodies, with only one or two exceptions, always appear wearing long black coats.

The original names of Nobodies are usually lost along with their hearts. They assume a new identity using an anagram of their old name plus an additional letter 'X.' Ansem becomes Xemnas, Braig becomes Xigbar, and so on.

Emotions
One of the most important points about Nobodies (pre-Dream Drop Distance) is their inability to feel emotions due to their missing hearts. Humanoid Nobodies are able to act as if they have emotions in order to fool others (and, as some would argue, themselves.) This capability for acting comes from the memories of the Nobody's previous life; essentially, they are able to remember how emotions work but cannot actually feel them. It should be noted that emotions are not the same thing as physical sensation. Nobodies are able to respond to external stimuli such as pain or touch. Additionally, a lack of emotion does not equate to a lack of skill, as many members of Organization XIII are very capable tacticians and combatants.

Whether or not Nobodies can have friendships or romantic relationships is a difficult and hotly debated topic within fandom. Friendship does seem to exist within the Organization, although some might describe them more as working partnerships. It may be argued that, similar to emotions, friendships amongst Nobodies are based around having previous memories of the concept. Romance is never delved into in any meaningful way, although there were occasions in canon when one Nobody did express flirtatious behavior with another (Larxene with Axel). There is no suggestion of homosexual attraction within the Organization, despite what AkuRoku fans would argue.

The Kingdom Hearts manga (which is considered noncanonical) argues that Nobodies do, in fact, feel emotions. Their lack of a heart, however, results in a constant feeling of uncertainty and emptiness.

Kingdom Hearts 3D: Dream Drop Distance revealed that Nobodies are capable of developing new hearts (and thus emotions) given time. This can be seen in the characters of Roxas, Axel, and Namine.

Nobodies in Badfic
Nobody!Sues and Stus will always have human-like appearances. Their names are usually nonsensical -- the anagramed original name is gibberish, even by Kingdom Hearts standards. They usually wield fantastic or 'cool' weapons, with the worst having gunblades or even their own Keyblades. More powerful Nobody!Sues will have control over some universal element in a manner similiar to the original Organization members. Particularly bad examples will simply use one of the powers already controlled by a preexisting member.

Nobody!Sues are prone to being romantically paired with canonical members of Organization XIII. Said pairing usually makes the canon in question wildly out of character.

Nobody Agents
Xericka is currently the only active Nobody agent.