Our plans have been dashed by you... far more times than I care to count. Now it ends. I will purge that light in you... with darkness!
Xemnas to Lea
Xemnas, the Superior of the In-Between (狭間の指導者 Hazama no Shidōsha?), is Xehanort's Nobody via Terra-Xehanort. He is Rank I within Organization XIII, and the ruler of The World That Never Was. He is the main antagonist of Kingdom Hearts II and Kingdom Hearts 358/2 Days, and later a member of the real Organization XIII, the main antagonistic force of Kingdom Hearts 3D: Dream Drop Distance and Kingdom Hearts III.
As the oldest of the Nobodies, Xemnas wields the power of nothingness, and channels this into his weapons, red blades of energy called Ethereal Blades, which extend from the palms of his hands. He commands the Sorcerer Nobodies. As the superior, Xemnas is the first member and founder of Organization XIII, with all other Nobodies under his control. He is able to manipulate Sora, Roxas, and Xion to use the Keyblade's power for himself. He also appears to be the most powerful, so much that even Marluxia would not dare to face him in Kingdom Hearts: Chain of Memories.
Despite his original name being Xehanort, he uses an anagram of his mentor Ansem the Wise's name due to Xehanort stealing the name prior to discarding his heart and body. Xemnas is a playable character in the Mission Mode of Kingdom Hearts 358/2 Days.
Being the founder of Organization XIII and apparently the oldest of Nobodies, Xemnas is truly emotionless—in every sense of the word—and does not even remember what it was like to have any feelings. He claimed that this allowed him to have a clear understanding of the heart, but, in reality, this had warped his mind into believing that only anger, hatred, and other negative emotions were what make up most of a heart.
His lack of emotion deprives him of remorse for his actions, as well as the loss of the other members of the Organization. The only thing he truly cared about was Kingdom Hearts and his desire for power, and even lamented it when it was damaged. However, on some occasions, he had appeared to value friendship, as he was shown to converse with the armor of Aqua in the Chamber of Repose, although, this is likely due to the influence of Terra, as he is, in a sense, Terra's Nobody.
Unlike the other members of the Organization, Xemnas did not seem to want Kingdom Hearts for a true existence. Rather, much like his Heartless counterpart, he wanted it to use it to obtain power and remake the universe in his image. This concept was furthered as Xemnas thought that nothingness was the source of much power, and does not seem to despise it in the slightest. This goal stemmed from that of one of his two original personas, Master Xehanort, whom also desired to unlock Kingdom Hearts for the same purpose in Kingdom Hearts Birth by Sleep.
In other matters Xemnas spoke with calmness and deep authority, strangely similar to Master Eraqus. He had a tendency to be overly melodramatic, making long-winded speeches, exaggerating his false rage and sorrow with wide sweeping arm movements and hand gestures, like many villains. While ridiculous in nature, his exaggerations were representations of his lack of emotion. He was very intelligent, overall, and knew how to manipulate others, particularly Sora and his friends for his own needs.
Xemnas's personality seemed to share traits from both beings who composed his original persona, Master Xehanort and Terra. From the former he inherited his manipulative nature and the ideas for the black coat and adding the letter "χ" to rename himself and his fellow Organization members. It is very hard to say how much he inherited from Terra, but there is at least the familiarity with Aqua's armor, to which he refers to as "friend", and his strong desire to find his other "friend" in Castle Oblivion, as he has had Saïx search for the Chamber he sleeps in. Another example was when Roxas fell into a comatose state, saying: "So, sleep has taken you again".
After being defeated one last time, Xemnas, while lamenting he was bested again, finally regains his emotions and realizes that he misses his companions and that he took them for granted. Due to his newfound feelings of loneliness, Xemnas states that a heart is just about pain but when Sora says that pain is part of being human, Xemnas gives the boy a praising smile for being strong enough to live on.
Like all the Organization members, Xemnas wears the standard black coat, gloves, and knee-length boots with silver trimming and high concave indentations in the top. He has orange eyes and tanned skin, much like his Heartless counterpart and his complete being, Xehanort. Xemnas's hair is long, reaching to about mid-back, silver in color, and some of it falls over his shoulders. His hairstyle is reminiscent of Xehanort's hair, including his bangs, the color, and the length. It also shares traits with Terra's hair, including its layered, messy look and the spike on the top of his head.
Because Xemnas was born from the body of Terra, his overall appearance is identical to Terra's, save for the silver hair, orange eyes, and older appearance resultant from having Xehanort's soul.
While commanding the World of Nothingness, Xemnas dons armor adorned with dozens of Nobody symbols. The shoulder pad on his left shoulder, helmet, crown, boots, knees, and breastplate all sport these designs. His crown and shoulder pad are gold, while the rest of the armor is colored in light shades of blue and silver. He has two silver belts on his waist and what seem to be white feathers on his right shoulder in place of armor. Several cords crisscross in front of his torso, connecting to massive, oblong pieces of armor worn on each arm. Xemnas's faceplate is beak-like in structure and he wears clawed, metal gloves.
He also wears black pants underneath the armor. Perhaps the most striking features of this armor are the odd, pulsating growths sprouting from Xemnas's right shoulder and both arms. These growths appear organic and are a mixture of red, orange, yellow, and white. While the larger one on his shoulder seems to connect Xemnas to his dragon-like Nobody battleship, the other two on his arms just lie on the ground, seemingly serving no purpose. This armored form, referred to as the Armored Controller, bears a striking resemblance to No Heart.
In his final section of his battle with Sora and Riku, Xemnas's appearance is unchanged, save for his cloak. His black coat is now white and is covered with intricate black designs that resemble the Nobody sigil.
As the leader of Organization XIII, Xemnas is the most powerful Nobody in existence, far more powerful than even the other members of the Organization, as even the arrogant Marluxia, who is himself a powerful member of the Organization in his own right, would not dare to fight him even alongside Larxene and Axel. It has also been confirmed that he is even stronger than Roxas at his full power, which was why Xion was so desperate for Riku to stop Roxas as she knows Roxas isn't strong enough to fight Xemnas and Riku himself stated that going after the Kingdom Hearts is suicide as it means fighting Xemnas and Xemnas would destroy Roxas. He is particularly feared by Vexen, the weakest member of the Organization, to the point of not daring to interrupt his time in the Chamber of Waking and the mere mention of Xemnas being enough to cause the high-ranked scientist to back down. Even Saïx, who is Xemnas's second in command and one of the most powerful members of the Organization, does not seem to be willing to fight him alone despite knowing of Xemnas's true plans and even with Axel, who is also a powerful member of the Organization in his own right, he still chose to operate in secrecy and recruit Xion and Roxas before challenging him. Xemnas is also the only one, apart from perhaps Saïx, who even Axel fears, who has been shown to be unafraid of facing other high-level members of the Organization such as Marluxia, Saïx, and Xaldin, therefore reluctantly going after Xion and Roxas when Xemnas ordered it.
As the most powerful and oldest of the Nobodies, Xemnas, in addition to having his subordinates's ability to fly and teleport, wields the power of Nothingness. He uses this to form his personal weapon by solidifying beams of Nothingness into blades of energy called Ethereal Blades that act to his will, allowing him to manifest and de-manifest them at whim and change their length, which he can either wield in close combat like real swords, not needing a hilt or handle to hold them, or fire them as laser-like projectiles, either from his hands directly or suspending them in mid-air first. He can make as many as he wants, even creating thousands as his desperation attack. Xemnas is also capable of using Nothingness to cast energy balls capable of exploding into orb-like force-fields as well as firing powerful lasers, which he can do from all directions. He can manifest a barrier capable of damaging Sora and use the barrier offensively by having it rush towards Sora or using it to trap him. In Kingdom Hearts 358/2 Days, Xemnas's limit break named All-Vanity consists of Xemnas summoning a barrier around himself that is impenetrable and can damage any enemy that touches it. Xemnas's Final Limit retains his barrier but Xemnas also creates two large powerful lasers from his hands that he fires around himself at a long range that can heavily damage any enemy. His control over Nothingness also allows him to turn even other Organization members into Dusks or destroy them if he wants to and he has absolute control over all other Nobodies, specifically the Sorcerers. In Kingdom Hearts III, Xemnas replaces his previous darkness and light-empowered hand-to-hand attacks with a Nothingness empowered swift spinning kick and he could release fissures of blue energy with his Ethereal Blades. He even proved able to effortlessly destroy Lea's Keyblade with a single surge of Nothingness.
In addition to Nothingness, Xemnas naturally has power over Darkness and in addition to the basic ability to open Corridor of Darkness, he is one of the few Organization members capable of employing Darkness in combat, able to encase Sora in a sphere of dark energy to slowly drain his health, surround himself in a ball of dark energy and move around at incredible speeds, and even generate enough darkness to cover the entire arena, doing so in his secret boss and final form. With the powers of Kingdom Hearts at his disposal, Xemnas not only gains stronger powers over darkness but also gains the powers of light, allowing him to generate thorns of black and white energy, summon crests of light able to fire beams of white energy and empower his kicks and punches with darkness and light, causing them to emit either shadowy or white energy.
Xemnas appears to have the ability to create pocket dimensions at will that he can control to his whim, as shown by how he warps himself and Sora while leaving the rest of his enemies in his castle to a realm of nothingness where only the Memory Skycraper stands and later on when he summons a small alternate dimension to ensnare and torture Axel by firing lasers all around him. While merged with Kingdom Hearts, it seems his "creation" ability becomes much more potent, as he is capable of creating an actual realm within Kingdom Hearts named the World of Nothingness and also manifesting a large dragon ship equipped with powerful laser-firing barrels as well as creating Bomb Bells and Spiked Rollers to guard the inner function of his ship and also to attack. He conjures and launches buildings and snowflake projections capable of firing lasers and even at one point generates a black hole to swallow Sora and Riku's ship. He also was capable of shapeshifting into a form for his final battle that gives him a robe that represents both light and darkness and greatly increases his power and allows him to create clones of himself. Even without having the powers of Kingdom Hearts, Xemnas still retains the ability to summon and launch buildings at Sora.
While facing Sora and the rest in his armor, Xemnas wields a large sword capable of dealing great damage with a single swing and by slamming it to the ground, he can generate a shockwave capable of pushing Sora and Riku away a great distance. He also has access to the powers and weapons of his fallen organization comrades, therefore capable of summoning Demyx's Water Forms to deal great damage, accessing Luxord's Fair Game, telekinetically suspending and having Xigbar's Sharpshooters fire lasers and Xaldin's lances blast wind, unleashing powerful shockwave from Saïx's Lunatic, and manifesting a ring of fire and Axel's Eternal Flames.
In all his boss battles, he displays outstanding agility and athletic prowess as well as excellent swordsmanship and martial arts skill, capable of unleashing relentless barrages of attacks from both his Ethereal Blades and even unarmed that are hard to block, preferring swift spinning kicks and. In terms of speed and agility, he is shown to be easily equal to, if not, superior to Larxene. Not only is he shown to be able to trade blows with Sora in his regular form, but in his final form, he is even able to overtake and disarm Sora as well as fight off both Sora and Riku when Sora had regained his weapons along with fatally injuring Riku before finally being defeated. His greatest feat was easily catching Lea's Keyblade strike by it's handle to prevent it from slashing him one-handed.
Xemnas uses weapons called Ethereal Blades (エアリアルブレード Eariaru Burēdo?, lit. "Aerial Blades"). They are beams of red energy and extend directly from the palms of his hands, without any hilt or handle. He can summon or disperse them at will, and is able to change their length as well. They are solid despite their appearance, and, despite seemingly lacking a cutting edge, are wielded like swords. The Ethereal Blades can also be used as projectiles and can suspend themselves in midair around a target before firing at them. As a desperation move, Xemnas can surround his enemy in darkness and fire an amazing amount of Ethereal Blades at them. Xemnas displayed superb prowess in swordsmanship using them, performing many swift and acrobatic combos with them.
The names of Xemnas's various Ethereal Blades seem to be references to iron-fisted leadership. Perhaps due to his preeminent power among the Organization, only one of his Ethereal Blades, Infinity, actually grants him a support ability.
Having been the Nobody of Terra Xehanort, who can use a Keyblade, it is safe to assume that like Roxas, who can wield a Keyblade due to being Sora's Nobody, he does have the ability wield a Keyblade if he wanted to but just couldn't due to having to conceal his connection to Xehanort as best as he could. His ability to use of Master Xehanort's Keyblade Armor during his battles with Sora and Riku further supports this.
- As pointed out in Director's Secret Report XIII, Xemnas is a "special nobody" like Roxas and Naminé. This may be from the fact that his original form had the hearts of both Terra and Master Xehanort.
- Xemnas is the last member to receive an English translation of his title. The opening movie of Kingdom Hearts 358/2 Days listed every member's title in the Japanese version, but these were not included in the English version until Kingdom Hearts HD 1.5 ReMIX.
- Kingdom Hearts Birth by Sleep Ultimania: "Xemnas gives Organization members names with an X in them. This has something to do with Master Xehanort’s interest in the χ-blade".
-  "Xemnas is the strongest and Roxas is considerably strong if you count his full potential."
- The meaning of the word "ethereal" is "not of the earth; heavenly".
- Nomura Interview "It's possible that [Xemnas] intentionally wasn't using [a Keyblade]"