Darkling

The Darkling is a Pureblood Heartless that appears in Kingdom Hearts χ.

Born from Keyblade wielders who succumb to the darkness in their hearts, these Heartless retain the ability to speak and access the Lanes between, but unlike their human forms, they do not draw power from the Book of Prophecies' fragments during battle.

Design
The Darkling appears as a mostly humanoid body, entirely black with minimal blue tint, similar to a more humanoid Shadow. Its head is round and spherical, with a red zigzag mouth and spherical, fully yellow eyes. Its arms and legs are thin.

The Darkling wears black clothes of slightly different color than its body, and, except for its shoes, the ends of the clothing have spiked tips on it, giving a torn visage to the outfit. On its head is a hoodie which has two spiral eye patterns on the front of the same red shade of its mouth. Protruding from the hoodie are two horn like antennae extensions with stripes on them that end bent into a zigzag. Wings also protrude from the Darkling. Two red barbed wires crossing into an X shape are laid on to its otherwise bare chest. It wears large, black gloves with five fingers, and each of those fingers has a gradient to red on the end from black in the middle. The gloves are held right by red barbed wires. It wears black vertically striped pants that are short and held up by a black belt. Finally, it has small black shoes held tight by red strings.

Kingdom Hearts χ
Outside the clock tower in Daybreak Town, and Skuld are attacked by a group of Darklings. The Heartless demand the Keyblade wielders give them their captured Lux, but they flee after a battle when a Nightmare Chirithy appears before them.

The dark Chirithy explains that the Darklings were once Keyblade wielders until they let darkness enter their hearts as a result of it taking their Lux away so wielders would not have fight over it.

Later, Nightmare Chirithy absorbs them after a battle.

Kingdom Hearts Union χ[Cross]
After crossing the world line, the Darklings managed to follow them into the data world. When the glitches begin appearing inside the Clock Tower, Player and Ephemer come across Ventus and soon are surrounded by a Darkling who utters "not you...", which confuses the trio. While traversing through the mysterious tunnel, Ephemer and Player encounter it again, with the Heartless muttering the same phrase it did before. They do battle, and the Darkling runs further into the tunnel, with Ephemer and the Player in close pursuit.

In Game Central Station, Ephemer goes after a Darkling entering Hero's Duty. Through following Ralph into the Cy-Bug Sector, Player meets up with Ephemer who was following the Darkling. Defeating the Darkling for the third time and hearing it say "not you", Ephemer is still perplexed on what it could mean. Before they had a chance to confront it, the Darkling gets eaten by a Cy-Bug, fusing them together. It flies off as the pair chase after it.

Finally catching up to it, Player and Ephemer manage to destroy it. Later, in Sugar Rush, after King Candy and the Cy-bugs are defeated, Player and Chirithy can still sense that the Darkling is still around and see that it has gotten much stronger since their last encounter. Having enough, Chirithy asks the Darkling why it keeps following them if they are not the ones it wants. The creature doesn't answer and is destroyed once again. However, Chirithy wonders if the Darkling was drawn to the Keyblade in the same way that the Cy-Bugs were drawn to the beacon in Hero's Duty. Chirithy continued wondering that if the Darkling was really after a Keyblade wielder.

During the confrontation between Darkness and the Union leaders, Darklings appear, with Ventus, who is currently comatose, as their target. Ventus wakes up and uses the light within his heart to destroy them.