Xemnas

Xemnas is the Nobody of Xehanort, the superior of Organization XIII and the ruler of The World That Never Was. Despite his original name being Xehanort, he uses an anagram of his mentor's name: Ansem, due to Xehanort stealing the name prior to discarding his heart and body. He uses the element of nothingness, and wields aerial blades. He also commands the Sorcerer Nobodies.

Xemnas will be a playable character in the multiplayer format of Kingdom Hearts 358/2 Days.

His complete being, Xehanort, may also have an appearance in Kingdom Hearts: Birth by Sleep, due to his possible connection to Aqua, whose armor resides in the Chamber of Rest (see below).

Kingdom Hearts: Final Mix
A Mysterious guy who appeared at Hollow Bastion

Kingdom Hearts II
"Organization XIII's Number I."

''He directs the group as its leader. ''

''In truth, he is the Nobody of Xehanort, who was apprenticed to Ansem the Wise. In secret, Xehanort studied the doors and the heart of all worlds, ultimately stealing his master's name, Ansem. When Xehanort became a Heartless, his Nobody Xemnas came into being.''

Xemnas is using Sora, collecting the hearts released every time a Heartless falls to his Keyblade.

A Test
Xemnas first appears in Kingdom Hearts: Final Mix, arriving at Hollow Bastion to see Sora after recruiting Roxas. The Princesses of Heart sense his incredible power, and Sora, Donald, Goofy, and the Beast go to the abandoned area where they fought Maleficent to investigate, and soon encounter Xemnas. He is at first intangible, and passes through Sora, causing him to experience many of his memories in rapid succession (a power seen again in Chain of Memories). Sora asks who the man is, and Goofy wonders if it is Ansem, and though Xemnas says he is familiar with the name, he does not clarify how or who he is (all the while, he speaks through his mind, rather than physically). He then launches an energy attack at Sora, who manages to deflect it (with some difficulty). Xemnas remarks how Sora looks like "him", and that he is not complete, but only confuses Sora. He then attacks the Keyblade wielder, intending to test his power.

Afterwards, he backs off, appearing to be defeated, but quickly abandons the facade. He finds Sora fascinating, and says that they will one day meet again and disappears, but not before making an ambiguous comment on how he is but a "mere shell".

Roxas
In the opening scene of Kingdom Hearts II, Xemnas is seen at a dark beach. Roxas soon joins him. Xemnas says that he has been to see Sora, also commenting on how the two look alike. Roxas asks just who he is, but Xemnas only explains just what he is. When Roxas repeats the question, Xemnas answers the question with his own question: "Do you remember your true name"?

According to Tetsuya Nomura, this scene is not truly real. Rather, it is a mix of all of Roxas' emotions, feelings, and desires.

They meet again
True to Xemnas' words, he and Sora meet again at Hollow Bastion, the same world he was first encountered, albeit restored, accompanied by Saïx, Xigbar, Demyx, Xaldin, and Luxord (although all of their faces are hidden by their hoods, and do not directly face Sora), although Sora doesn't recognize him or his cloak from their first encounter. They taunt and mock him, only furthering Sora's desire to defeat them. Xemnas makes an empty joke about how he thought they could've been friends, and then leaves.

From there on in, Xemnas remained at his castle while his group's members traveled to make sure Sora stayed on track, while increasing the number of Heartless for him to fight.

The Heartless Invasion
Xemnas is not seen again until the Heartless invasion, arriving to the Computer room to access the Chamber of Rest before appearing to look down upon the Heartless army that had temporarily halted in the Great Maw. King Mickey, upon seeing his face, immediately remembers just who's Nobody Xemnas is: Xehanort, the apprentice of Ansem the Wise. Xemnas then runs off, and King Mickey gives chase, though Sora, Donald, and Goofy are impeded from following by the Heartless.

After an exhausting battle, the three make their way to the cliff overlooking Villain's Vale; finally catching up with the King. Sora demands to know where Riku and Kairi are. Xemnas claims to know nothing of any "Kairi", but for Riku, Xemnas tells Sora to ask his King. Then, he vanishes into a corridor of darkness, but not before King Mickey follows him in.

Kingdom Hearts II
Xemnas again appears in the World That Never Was, standing upon the highest tower of the Nobody castle, asking Kingdom Hearts to share its power with all Nobodies. Saïx then appears, asking whether Kingdom Hearts is complete. Xemnas says it will be soon, and allows Saïx to end their game and finish off Sora and his companions.

After all Organization members save for himself had been eliminated, Xemnas comes to greet Ansem the Wise, who had been attempting to digitally seal Kingdom Hearts away. The former pupil mocks his teacher, stating that he is the source of all Heartless, for inspiring him to go where Ansem himself did not dare to venture. Though Ansem admits that his foolishness was the source of much misery, he questions Xemnas on how this was what he had been seeking. Xemnas says it is that and more, and reveals his plans to create a brand new world, one heart at a time. He admits he thought that Ansem would praise him, but instead only held him back, consumed by the jealousy he had for his student. But he understands that Ansem was not able to control his heart.

Ansem scoffs at this, stating that they both claim to understand the heart, but actually know as little about it as they had in the very beginning. He declares passionately that Xemnas will fail and so will his world, and tells Riku to finish what he had started, and says farewell to the King. Then, the machine Ansem had been using explodes, and Xemnas retreats just as the bright light envelops the area. The explosion also caused severe damage to Kingdom Hearts, causing countless hearts to rain down upon the world, which would transform into Heartless upon touching the darkness that coated the world.

Sora and the others then travel up to the very top of the tower, where Xemnas lamented over the damage done to Kingdom Hearts. He asks the three Keyblade wielders to fetch him more hearts, and when they refuse, he asks why they hate the darkness. King Mickey responds that they don't hate the darkness, but just that it's "scary". But he knows that the world is made of both light and darkness, and then wonders why they really are afraid of the darkness. Riku adds that it is because of who  or what's lurking inside that darkness.

Xemnas then asks another question: if they accept the darkness, yet choose to live in light, why do they loathe those who are nothing, having been turned away from both the darkness and the light? Riku answers that it's because they endangered the worlds, and Xemnas tries to justify it with the fact that they had no choice. However, Sora does not believe this, stating they had no remorse over their actions anyway. Xemnas chuckles, stating that it is very true, and proceeds to face Sora one on one in an arena of nothingness, with Memory's Skyscraper towering above them.

Xemnas appears defeated, returning Sora to the Castle That Never Was, but Xemnas is still alive and well, basking inside Kingdom Hearts, urging it to join forces with him to gain the power needed to destroy their common enemies. Sora and the others try to stop him, but it is too late, and Xemnas is absorbed into Kingdom Hearts. Fortunately, the worlds created a door for Sora and the others to enter, for they wanted them to be the guardians of their destiny. They then follow Xemnas into Kingdom Hearts, but they see that Xemnas has taken its power and transformed the realm into a place resembling the World That Never Was with a giant fortress in the middle. He says that their hearts have led them to their deaths, seeing that it may not be worth following one's heart, and takes note of it, before hurling a building at them. This causes Kairi and Mickey to be separated from the others, but even so, Sora and co. defeat Xemnas in his knight-like form. He thinks that he needs more hearts and more rage, but Sora tells him that hearts are more than just anger or hate, and asks if he remembers, which he doesn't, before seemingly fading back into the darkness.

Ultimate Destruction
With the help of Naminé, Kairi, Donald, Goofy, and the King get safely to Destiny Islands, but before Sora and Riku can follow, Xemnas attacks once more; having merged with a gigantic mechanical dragon. After another difficult battle, Xemnas takes Sora and Riku to a realm of nothingness, with Xemnas wearing a robe representing both light and darkness. He says that if both light and darkness are eternal, then so too must be nothingness. Riku and Sora says this is true, but that does not mean Xemnas is eternal. They then share a very tense battle, with Xemnas wounding both Sora and Riku with various attacks. This is also the only time you ever play as Riku, during a point in the battle where Xemnas tries to suck Sora's Heart out, and Riku has to save him. Riku is badly injured during the fight, so Sora batters Xemnas into submission with his and Riku's Keyblades. Sora and Riku then finish him off. Xemnas fades into darkness, thus ending the threat of Organization XIII and the madness of Xehanort forever, making him the last organization member to fall.

Personality
Being the founder of Organization XIII and apparently the oldest of Nobodies, Xemnas is truly emotionless and does not even remember what it was like to have emotions. He claims that this allows him to have a clear understanding of the heart, but in reality this has warped his mind into believing that only anger, hatred, and other negative feelings make up a heart.

Not to mention, his lack of emotion gives him absolutely zero remorse over his actions, as well as the loss of the other members of the Organization. The only thing he truly cares about is Kingdom Hearts and his desire for power, and even laments it when it is damaged. Unlike the other members of the organization, Xemnas does not seem to want Kingdom Hearts for a true existence. Rather, he wants it to use its' power to become a god-like entity and take control of the universe. This concept is furthered as Xemnas thinks that nothingness is the source of much power and does not seem to despise it in the slightest. He intended to combine this power with the power of hearts from Kingdom Hearts to become invincible.

In other matters Xemnas speaks with calmness and deep authority. He has a tendency to be overly melodramatic making long-winded speeches, exaggerating his false rage and sorrow with wide sweeping arm movements and hand gestures. While ridiculous in nature, his exaggerations are representations of his lack of emotion. He's very intelligent overall, and knows how to manipulate Sora.

The Superior
Xemnas, as the superior, is the first member and founder of Organization XIII, with all other Nobodies under his control. He is the most powerful member, so much, that Marluxia would not dare to face him even with the support of Axel and Larxene until Sora was completely under his control. Furthermore, Vexen immediately complied with Marluxia's order to eliminate Sora when he made the empty threat that he would report Vexen's failure to the Superior. He also appears to be the Organization's most intelligent member.

In Battle
As the leader of Organization XIII, Xemnas wields the element of nothingness, but his weapons seem to be made out of pure energy. His weapons are called Aerial Blades, two red blade-like weapons that form from his hands. In addition, Xemnas can shoot dagger-like versions of the Aerial Blades in rapid succession, become intangible for short periods of time, create powerful spheres of nothingness, create barriers, and use an attack called "Invitation to Nothingness", which slowly drains a person's life force until they die. Xemnas later uses variations of the weapons of the other Organization members to fight when he dons his armor.

In the final battle in Kingdom Hearts II, Xemnas goes into his final state. His abilities become far beyond that of his usual self; speed, power and stamina all increase dramatically. He creates an alter-image of himself, summon torrents of white and black thorns, much like Twilight Thorn, dash around with amazing speed and shoot multiple lasers that pelt his opponent. In addition, Xemnas can ensnare opponents in a sphere of dark energy that slowly eats away at their health (possibly trying to rip out their heart, as evidenced by the phrase, "Can you spare...a heart".) This attack was impossible for Sora to block or break free from, and it would have killed him if Riku didn't save him. But perhaps his greatest ability is to engulf the entire surroundings pitch black, and then summon thousands upon thousands of Aerial Blade lasers that surround their target, forming a dome, and then immediately barraging them from all sides.

In Kingdom Hearts: Final Mix, in his encounter as the Unknown, Xemnas also had the ability to encase himself in a blue ball of energy that made it impossible for Sora to attack him, and would also fire out a set of powerful laser. The ball would follow Sora around if he ever to tried to get away from it.

Trivia

 * Strangely, Sora doesn't seem to recognize the Organization cloak from his first encounter with Xemnas at Hollow Bastion. However, this may also be an effect of the loss of memories from his time at Castle Oblivion. This is backed up by the fact that Sora, despite DiZ and Naminé's restoration efforts, still has forgotten his abilities, such as his magic.
 * Xemnas is the only known Nobody whose name is not an anagram of his own with an added X, but rather Ansem the Wise's name, which he took for himself.
 * Roxas' battle with Riku, as seen in Another Side, Another Story, involves him running up the side of Memory Skyscraper and passing by Riku as he leaps off. This is mirrored in Sora's battle with Xemnas, with Sora taking Roxas' place and Xemnas taking Riku's.
 * Because of his confirmed playable appearance in 358/2 days, Xemnas has the distinction of being one of only two characters in the entire series (the other being Marluxia in Kingdom Hearts: Chain of Memories) to be both a playable character and final boss. However, if Riku is the end boss of said game, he will be a playable character at the end of Kingdom Hearts II and a final boss in Kingdom Hearts 358/2 Days.

Quotes
Most of Xemnas' lines were either changed or removed from the Japanese version. Here are the original lines, and their English counterparts.