Xehanort's Guardian

Xehanort's Guardian is a dark entity, similar to a Pureblood Heartless, which is used by Ansem, Seeker of Darkness throughout the Kingdom Hearts series. First created by the original Xehanort and used to battle Aqua, the Guardian is also temporarily used by Riku when he takes on the form of "Ansem" during the battle with Roxas. The Guardian serves not only to protect Xehanort from attacks, but also to fight for him when needed.

Kingdom Hearts Birth by Sleep
Having lost his first battle against Aqua, Terra-Xehanort's great rage causes the Guardian to spawn behind him. The two dark entities then team up to challenge Aqua one final time. Upon Terra-Xehanort's second defeat at Aqua's hand, Master Xehanort attempts to force what remains of Terra out of him by unlocking his heart. However, the Guardian reappears and begins to fade, opening a portal into the Realm of Darkness, which it and a severely weakened Terra-Xehanort fall into. Aqua then dives in after them and sacrifices both her armor and Keyblade to save her old friend Terra's body.

Kingdom Hearts
After conversing with Sora over the true nature of the heart, Ansem, Seeker of Darkness proceeds to summon his original persona's Guardian, preparing to battle Sora due to the Keybearer's naïvety. The Guardian later appears alongside Ansem during his second battle with Sora, again transforming and increasing in size to become part of the World of Chaos. The Guardian, along with the rest of the World of Chaos, is destroyed at the hands of Sora, Donald, and Goofy after the climatic battle.

Kingdom Hearts: Chain of Memories
After Riku emerges from the twelfth basement of Castle Oblivion, Ansem appears before him and attempts to retake his body. However, Riku chooses to fight rather than submit, enraging Ansem, who summons his Guardian and attacks.

Later, Riku reaches the first basement of Castle Oblivion and uses Naminé's Castle Oblivion World Card to bring forth Ansem. Ansem creates around them a facsimile of Kingdom Hearts itself, and again summons the Guardian, who attempts to crush Riku with a swing of its fist. However, Riku is able to defeat both Ansem and his Guardian, and he emerges from the battles having conquered his inner darkness.

Kingdom Hearts 358/2 Days
Realizing his loss to Roxas is inevitable, Riku unleashes the dark power that is Ansem, Seeker of Darkness that he had been holding back from within his heart. After transforming into a pseudo-Ansem, Seeker of Darkness form, Riku uses the Guardian to grab Roxas by the shoulders and squeeze him to the point of unconsciousness. This then allows Riku to take Roxas to DiZ as assigned, the only downside being the fact that he is stuck in the form of Ansem, Seeker of Darkness.

Abilities
The Guardian has many dark powers with which it assists the one it is paired with in battle. It also possesses great physical strength, impervious to all damage. While it tends to stay behind its host, it can be commanded to detach itself from that host to attack its victims. Able to latch onto these opponents and drain their HP, the Guardian can also hit them with bursts of energy spawned from its fists, mighty punches, and even spheres of energy. Similar to a Pureblood Heartless, the Guardian's most devastating ability allows it to sink into the ground, creating massive shockwaves every time it re-emerges. The Guardian also has the power to shoot disc-like projectiles at enemies, greatly multiplying the host's powers with its own as they double-team opponents to ram them with brute force while shining with a dark aura. In its World of Chaos form, the Guardian becomes more of a defense mechanism than one of offense, able to summon Bit Snipers to distract opponents and beat its massive wing-like arms to create large whirlwinds with the purpose of blowing enemies away. It can also drain an opponent's MP. While it is only when the Guardian is paired with its host that it is a formidable opponent, it is shown to hold its own quite well without influence, mercilessly attacking the opponent without ceasing.

Paired with Terra-Xehanort
When paired with Terra-Xehanort during the final battle with Aqua, the Guardian will do most of the attacking, creating small shockwaves as it re-emerges from dark portals on the ground, slamming Aqua into the ground after carrying her high into the air, should the shockwaves make contact with her. The Guardian can latch onto Aqua, the Keyblade Master only able to free herself when the player rapidly taps. The Guardian can deal a powerful punch, release twin columns of energy from its fists, and even shoot twin energy spheres from each hand. When very little of Terra-Xehanort's HP remains, it will warp Aqua to a light realm. The Guardian will attempt to drive Aqua away from Terra-Xehanort (who now bears the appearance of Terra) with its energy sphere attack, but if she gets past it and makes it to Terra-Xehanort's location, she can activate a special Deck Command called Dual Limit that will deal impressive amounts of damage to the Guardian by allowing Aqua to team up with Terra-Xehanort and shoot it with an immense amount of light energy.

Paired with Ansem (Battle I)
When paired with Ansem, Seeker of Darkness, the Guardian will immediately go on the offensive in battle, punching opponents if they come too close or bombarding them with dark projectiles if they are out of attack range. On Ansem's command, the Guardian will appear in front of him, preventing him from being damaged. However, Aeroga can still hit Ansem if one runs around to his location. The Guardian may also obey Ansem's command to leave him and attach itself to Sora, a "?" occasionally appearing over Sora's head once this occurs. If is pressed when this icon is on the screen, the Guardian will latch onto Sora and drain a large amount of his HP. It will eventually return to Ansem in the end, however. It is because of this attack that the player must use careful timing of the Dodge Roll ability, as well as use Curaga when necessary. Guard can be used to earn Tech Points when Sora deflects the dark discs the Guardian shoots back at it.

Paired with Ansem (Battle II)
When Ansem and the Guardian face Sora on his own, their moveset will be identical to that of the first battle. However, the Guardian and Ansem can now use some new, devastating attacks. The first involves the Guardian and Ansem jetting across the battlefield, dealing damage as they collide with Sora. Either Guard or Aeroga can be used to halt the Guardian and Ansem. The second is, by far, the most damaging, the Guardian sinking into the ground on Ansem's command and creating short-ranged shockwaves as it respawns in an attempt to attack Sora. Dodge Roll can be used to avoid the Guardian, as well as the large burst of energy that results in the Guardian returning to Ansem.

As the World of Chaos
The Guardian will not attack in the form of the World of Chaos. All it will do to aid its master Ansem is create large gusts of wind to blow Sora away. It can also summon Bit Snipers, which relinquish large and much-needed HP balls when defeated.

Paired with Ansem (Battle I)
During the first battle between Ansem, Riku, and the Guardian, Ansem will only shoot bursts of energy while the Guardian bombards Riku with punches. In Kingdom Hearts Re:Chain of Memories, however, the Guardian aids Ansem as he teaches Riku how to perform a Card Duel. The Guardian will only deal punching attacks during this "battle", as well, he and Ansem not taking damage as they did in the original Kingdom Hearts: Chain of Memories.

Paired with Ansem (Battle II)
During Riku's second battle with Ansem and the Guardian, the gloves are off. While Ansem shoots bursts of energy, the Guardian will punch at Riku, collide with him as he and Ansem fly at him shining with dark energy, or even create shockwaves as it sinks into the ground and re-emerges beneath Riku, hitting him several times. In Kingdom Hearts Re:Chain of Memories, it is the Guardian who launches the bursts of energy from its fists, also using the dark projectile attack from Kingdom Hearts. The shockwave desperation attack also has the added energy burst effect seen in Kingdom Hearts, as well.

Design
The Guardian has an ink-black, muscular, humanoid form with a partially bandaged head that hosts relatively human features, baring some resemblance to Master Xehanort. It has yellow eyes gleaming above a mouth filled with sharp teeth, as well as two long antennae spouting from the top of its head. A hole appears in-between more bandages on the torso in the shape of a heart, much similar to the heart shaped hole that appears in the [Darkside] Heartless. It lastly has very large hands, its torso coming to a tail-like point that fades away into its host's body.

While part of the World of Chaos, the Guardian mutates, its antennae becoming long horns, the rest of its body distorted by the darkness to look more muscular and ominous. Blue orbs rest on its shoulders, faint golden eyes also on the chest. Red tendrils extend from the back, attaching to the Guardian with a snake's head-like attachment. Its hands become massive wings, and an extension similar to a scorpion's stinger juts out of its back. The torso also appears more skeletal, with multiple ribs and vertebrae showing.