Unversed

The Unversed (アンヴァース), meaning "those who were not well-versed in their own existences", are the main enemies of the game Kingdom Hearts Birth by Sleep. They are, in essence, "the opposite of human life" and grew from the negative emotions produced when Ventus and Vanitas were separated from each other by Master Xehanort. Immature beings, they are a part of Vanitas's feelings, as well. It is because of this that the dark enigma is able to control them.

As stated by Vanitas himself, the Unversed were spread across the worlds specifically to be fought off by Terra, Ventus, and Aqua, ultimately making the trio stronger in the process. The sentiments of all defeated Unversed eventually returned to Vanitas in the end, the creatures disappearing upon Vanitas's destruction. By every and all accounts, the Unversed were extensions of Vanitas himself, and part of his power and influence - effectively making him the "first and original Unversed".

Kingdom Hearts Birth by Sleep
Around the same time as Master Xehanort's leave from the Land of Departure, the existence of the Unversed was brought to the attention of Master Eraqus by the Keyblade master's old friend, Master Yen Sid. Eraqus then sent two of his three apprentices, Terra and Aqua, on a quest to find Master Xehanort and stop the Unversed threat. He did not plan on his youngest apprentice, Ventus, trailing after his two friends, and it was on Ventus's quest that a final battle with the embodiment of his darkness, the mysterious Vanitas, would reveal the truth about the Unversed and how they came to be.

Vanitas revealed that the Unversed were his creation, and since he was a human created from the purest, most raw form of darkness, he could manipulate the negative thoughts and emotions of people. He spawned them as Unversed and spread them across the worlds, furthering his goals.

Appearance
Several varieties of Unversed appear over the course of Kingdom Hearts Birth by Sleep. Emotion was a key component in their conception and design. Thus they are seen with smiling, angry, and crying "faces," referring to the shape of their red eyes, which all Unversed share. The emblem most Unversed are christened with is also meant to represent a heart that expresses emotion.

Trivia

 * Due to a translation error, the Unversed were previously known to English audiences as the "Unbirths".
 * The Unversed are the only enemy species to be controlled by a single entity: Vanitas.
 * The Unversed are also the only enemy species not to have a playable character, unlike the Heartless (Sora's Heartless) and the Nobodies (Organization XIII).
 * Chronologically, Unversed are the second of the "three enemies" listed in the secret ending of Kingdom Hearts Final Mix, Deep Dive. This is most likely the case, as the Heartless were created first (there have been Heartless for as long as there have been hearts), and the Nobodies third. Vanitas, and therefore the Unversed, were born after Ventus fell to a pack of Neoshadows summoned by Master Xehanort.