Dark Hide

The unnamed Heartless, nicknamed "Red Eye" by the fans, is a Pureblood Heartless that appears in Kingdom Hearts Birth by Sleep Final Mix. It is the boss of the Realm of Darkness, and is fought by Aqua.

Design
At first nothing is seen of the unnamed Heartless, except by a pair of glowing red eyes and the black silhouette of its body. During the succeeding stages of its battle, its full body is revealed. It is a massive creature that slightly resembles the Dark Thorn. It has a dark-purple body with purple spikes running down its back as well as a purple mane around its head, a purple tail, claws, and legs. There are chains that bind its two front claws.

Kingdom Hearts Birth by Sleep
While making her way through the Realm of Darkness in an attempt to return home, Aqua is stalked unseen by the Heartless. Noticing the Heartless's presence, Aqua draws her Keyblade and the Heartless attacks, knocking her down. At first she mistakes it for an Unversed, but quickly realizes it is something else. She then engages the Heartless in a fierce battle, emerging victorious.

Strategy
The unnamed Heartless is a fast, fierce, and unpredictable opponent. In the first phase of the battle, the Heartless attacks from within the darkness, visible only by its glowing red eyes. The boss will attempt to charge at Aqua, and when it does the battle shifts to its point of view, making it hard to dodge. The Heartless also attacks with savage claw swipes and tail spins. After dealing significant damage to the Heartless, it will reveal its true form, starting the next phase of the fight.

The second stage of the battle is the same as the first, with the exception of the new attacks in the boss's arsenal. The boss still retains its claw swipes and spin attacks, but can now charge at Aqua, leaving a trail of flames in its wake. Also, the Heartless's movements become more erratic, making it hard to land hits. However, the Rhythm Mixer Command Style finisher deals great damage to the boss. After another round of combat, the Heartless unveils the rest of its attacks.

In the final round of the fight, the Heartless now uses red, blue, and green afterimages of itself for offensive and defensive purposes. It may spin around Aqua, its afterimages charging at her while it slams the ground, creating a shockwave. The boss can also shoot dark energy orbs that, after a few seconds, expand, damaging Aqua if she steps to close. It also utilizes a variant of the Mega Flare command, wherein it shoots a large fireball at Aqua. With some patience, Cure and potion commands, and high HP, the Heartless will eventually fall.

Attacks

 * Claw Swipes: Fast swipes with its claws
 * Tail Whip: Spins around, hitting Aqua with its tail
 * Buzz Saw: A damaging midair flip
 * Fire Charge: Charges at Aqua, leaving a trail of flames in its wake
 * Shadow Bomb: Shoots orbs of dark energy which expand into damaging force fields
 * Mega Flare: Shoots a large fireball
 * Illusion Spin: Uses its afterimages to charge at Aqua, while it attacks from above
 * Illusion Slash: Each of its afterimages attack with their claws