Xehanort's Guardian

The Xehanort's Guardian is a minor antagonist in the Kingdom Heart Series. It's a dark enity in a similar fashion to a Pureblood Heartless, and is a boss in several Kingdom Hearts games, mostly during the boss battle with Ansem.

Kingdom Hearts Birth by Sleep
Having lost his first battle against Aqua, Terra-Xehanort's rage causes the Guardian to emerge from Terra-Xehanort's shadow. The dark entity then teams up with Terra-Xehanort to challenge Aqua in a final battle. Upon Terra-Xehanort's second defeat by Aqua's hand, Master Xehanort attempted to force what remains of Terra out of him by unlocking his heart. However, the Guardian reappears but was beginning to fade. With it's last strength, the Guardian opened a portal into the Realm of Darkness, which it and a severely weakened Terra-Xehanort fell into. Aqua processed to dive in the Realm and sacrifices both her armor and Keyblade to save Terra's body.

Kingdom Hearts
After conversing with Sora over the true nature of the heart, Ansem proceeds to summon the Guardian, preparing to battle Sora due to the Keybearer's naïvety. The Guardian later appears alongside Ansem during his second battle with Sora. The Guardian then processed to transform and increasing in size, to become part of the World of Chaos. The Guardian, along with the rest of the World of Chaos, were destroyed after Sora and his friends defeated them their final battle.

Kingdom Hearts: Chain of Memories
After Riku emerges from the twelfth basement of Castle Oblivion, Ansem appears in front of him and attempts to retake his body. However, Riku chooses to fight rather than submit. Enraging Ansem, summoned his Guardian and processed to attack Riku. Riku was able to defeat both Ansem and the Guardian, and Ansem disappeared.

Later, Riku reached 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 summons the guardian again to attck Riku. The Guardian attempts to crush Riku with a swing of its fist, but Riku was 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 Ansem's darkness that he had been holding back from within his heart. Riku, now in Ansem's form, summoned the Guardian, and used it to grab Roxas by the shoulders and squeeze him to the point of unconsciousness. This then allows Riku to take Roxas to Ansem the Wise as he was assigned, the only downside being the fact that he is stuck in the form of Ansem.

Kingdom Hearts 3D: Dream Drop Distance
In the sleeping version of The World that Never Was, Ansem appears in front Riku. Ansem attempted to persuade Riku, again, to open himself to Darkness and allow his possession. However, Riku chooses to fight and vanquish his inner Darkness, causing Ansem to surround them in Darkness and summon the Guardian. After a first battle, Ansem allows the guardian to take control, growing larger and transforming into a greater threat. Despite the Guardian's new power, Riku was able to defeats the Guardian again.

Later in the real world, Ansem summons his Guardian to prevent Riku,King Mickey, and Lea from rescuing Sora from Master Xehanort. The Guardian managed to grab both Mickey and Riku to prevent them from escaping, but were defeated when Donald and Goofy accidentily fell on the Guardian's Head after warping in with the Star Shard.