“It happened when you and I were split into two. The negativity took shape as these monsters. They are what I feel—a horde of fledgling emotions under my control.”
―Vanitas, explaining the existence of the Unversed to Ventus[src]
The Unversed are the main enemies of Kingdom Hearts: Birth by Sleep. They are considered "the opposite of human life" and grow from the negative emotions produced when Vanitas was created from Ventus. It is because of this that Vanitas is able to control them. By all accounts, the Unversed are extensions of Vanitas himself, and part of his power and influence—effectively making him the first and original Unversed.
Before Kingdom Hearts: Birth by Sleep
The Unversed first came into being soon after Vanitas was created by Xehanort from the extracted darkness in Ventus' heart. Out of mixed feelings of self-hatred that spawned the first of them, Vanitas attempted to destroy the creatures but re-absorbed them. As a result, the negativity of the defeated Unversed worsens Vanitas' mental state as more Unversed are created in a vicious cycle that lasted until Ventus came in contact with Sora's heart. After being forced to part ways with Ventus, Vanitas is forced to fight the Unversed in another cycle of pain and suffering before finally breaking down from the strain and deciding to aid Xehanort to create χ-blade so his pain can ceased to be.
After the Mark of Mastery conducted by Eraqus, Vanitas unleashes the Unversed on the worlds as part of Xehanort's plan to get both Terra and Ventus to leave the Land of Departure. Across the worlds, the Unversed appear before and aid those with negative thoughts and emotions. Ultimately, prior to fusing back into Ventus' body as he has some of his extensions hold him at bay, Vanitas reveals the Unversed's origins and that their primary purpose was to ensure that Ventus would grow stronger with every confrontation. With Vanitas back in Ventus' body, the Unversed ceased to be.
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.
List of Unversed
*note* The ones in bold are bosses.
Red Hot Chili
Blue Sea Salt
Jelly Glee Tea
Spirit of the Magic Mirror
Iron Imprisoner I
Iron Imprisoner II
Iron Imprisoner III
Iron Imprisoner IV
Unlike Heartless bosses, whom are enveloped in light when defeated, the Unversed bosses are consumed in a dark flame when vanquished.