Saïx

Saïx, the Luna Diviner, is number VII in the Organization and the last of Xemnas's companions to fall to Sora, as well as the apparent second-in-command. He derives power from the Moon, utilizes a claymore in battle, and controls the Berserker Nobodies.

Saïx, along with all other members of Organization XIII, will be a playable character in the multiplayer mode of Kingdom Hearts 358/2 Days.

Kingdom Hearts II
"Organization XIII's Number VII." He was in pursuit of the renegade Axel, but for some reason seemed more concerned about Sora's well-being.

''Saix has no heart, but knows all too well how to injure one. No doubt his poise belies a more savage nature. He also insinuated he knew something about Riku.''

Hollow Bastion
Saïx first appears in Hollow Bastion, along with all surviving Organization members save Axel, to taunt Sora. He remarks "You're doing well", but like the others (save for Xigbar), does not confront Sora.

Twilight Town
Upon Sora's second visit to Twilight Town, the trio fight off several Nobodies that were attacking Seifer and his gang. After they save him, Saïx appears before them, applauding their battle skills. He warns them of a traitor in the Organization: Axel, and he says that he might be in Twilight Town somewhere. Sora insults the Organization, remarking on how they're "not a very organized Organization". Saïx is unfazed, and tells Sora to watch his back, for Axel will stop at nothing to turn him into a Heartless. Sora is not worried, leading Saïx to remark that the Organization would want nothing to happen to Sora, also saying they know how to "injure a heart". He then opens a portal behind him, and Sora thinks of jumping in after him, though Saïx overhears this and advises not to do so, lest he end up like Riku.

Sora inquires as to what he means, but Saïx immediately leaves to report to Xemnas that he suceeded in placing Sora in a state of confusion and frustration to keep him going toward their goal. But Saïx state that Axel may prove a thorn in their side, with Xemnas giving him orders to deal with Axel.

The Heartless Invasion
Saïx next appears in Hollow Bastion during the Heartless invasion, interrupting Axel and Sora's conversation, and forcing the traitor Nobody to flee. Saïx ensures that Axel will be rightly punished, but Sora only wants to enter the realm of darkness to rescue Kairi. Saïx asks Sora to prove just how much he cares about Kairi, and prove it he does, as he actually gets onto his knees and begs. Seeing Sora's devotion to the Princess of Heart, Saïx refuses Sora's wish, eliciting rage from the Keyblade master. Saïx only uses this to his advantage, ordering Sora to destroy more Heartless, so that the hearts held within them are released by the Keyblade. Then they may flock to Kingdom Hearts, which the Nobodies can use to truly exist once it is finished.

At that moment, Maleficent appears, declaring that Kingdom Hearts will belong to her. She summons more Heartless to attack Saïx, despite Sora's protests, but Saïx calmly summons several Nobodies to destroy the attacking Heartless. Maleficent then puts herself between Sora and the Nobodies, telling him to devise a way to vanquish the Organization. Soon, she is overwhelmed and disappears, allowing Saïx to resume having Sora release more hearts. But before that could happen, Sora, Donald, and Goofy are rescued by a portal of darkness that swallows them up (presumably Maleficent's doing).

The World That Never Was
In the Japanese and Greatest Hits version of Kingdom Hearts II, Saïx is seen again when you make it to Crooked Ascension. He aims to confront Kairi and Namine, but Riku (still cloaked and in the form of Xehanort's Heartless) attacks him from behind. Saïx does a back flip in the air, and lands a few feet away. Riku then slams him up against the wall. However, Saïx opens up a portal behind him and sinks away into the wall with a smirk.

The Final Battle
Saïx again appears in the World That Never Was to Sora, who had managed to work their way through the Organization's floating fortress. The Organization member says that Kairi no longer needs him and makes a cryptic remark about a "friend from the darkness". Sora is not deterred by Saïx's manipulative comments, but Saïx is not concerned. He tells Sora that Kingdom Hearts is nearly done, pointing to a heart-shaped moon in the sky. He then summons more Heartless for Sora to destroy, but his attention is quickly turned to Maleficent, who has also infiltrated the castle along with Pete. He takes this in stride, and soon after vanishes to check on Kingdom Hearts.

Saïx appears to Xemnas, who is watching Kingdom Hearts come closer to completion. He asks the Superior if he can end the charade and Xemnas allows him to do so, as Sora's part in their plan is done with and can now be killed. Saïx smiles and remarks that he's waited so long to hear that.

Saïx awaits Sora, Donald, Goofy, Riku, and Kairi in a room with a direct view of Kingdom Hearts: Addled Impasse. He calls Sora by the name of "Roxas", saying only he could've made it this far, though Donald vehemently states that he is Sora. Saïx does not care, and summons his weapon, simply says "Different name, same fate", and creates a powerful shockwave with sheer strength alone. The attack does no harm, but it manages to push away Kairi and Riku, separating them from the battle. He then confronts Sora, Donald, and Goofy, at last revealing the savage nature that lay hidden under his calm exterior.

However, despite Saïx's great strength and skill, he loses the battle. Defeated and mortally wounded, he slowly steps towards the moon. He sadly asks Kingdom Hearts where his heart is, before fading back into darkness.

Personality
Next to Xemnas, Saïx is possibly the most "nobody-like" of the Organization and despite claiming to remember what possessing a heart was like, behaves mostly as a cold, emotionless and efficient operative. In almost all of his appearances, he acts very calmly, never losing composure in even the direst of situations. He appears to be the most intelligent member of Organization XIII next to Xemnas.

But this calm exterior belies a savagery. In his final confrontation with Sora under the heart-shaped moon of Kingdom Hearts, he becomes a berserk force of destruction (a play on the madness inducing effects of the moon, hence the term lunatic). Unlike his calm and reserved manner that is usual of him, in battle he roars, shouts, and attacks like a ferocious beast with no sense of self control. In fact, he is practically psychotic with the influence of the moon.

Also, During Saïx's conversation with Xemnas, he asks if he "can end this charade." Xemnes replies with an "indeed", and Saïx gives a rather evil smirk. This implies that Saïx was made to act calm, just for the missions with Sora.

Fighting Style
Saïx is a very powerful member of the Organization. Throughout most of the game, he is seen as a calm and collected figure, but in battle, he is a wild, dangerous beast. True to his use of brute strength, he employs a claymore, using it to draw upon the power of the moon. When he does this, he temporarily gains a dramatic increase in power, becoming nigh invincible. His attacks form blue flames, create blazing paths and walls, as well as gigantic shockwaves, adding to his already formidable strength. In Berserker mode, each of his attacks leaves his claymore stuck in the ground, and instead of retrieving it, easily forms new ones. However, this allows Sora to use the old claymores against him, which when used properly, can cancel out Saïx's powered form. It should be noted that the longer the claymores he's thrown is not used, the longer he'll remain in his "Beserker" mode.

The Nobodies under his command, the Beserkers, follow his attack style, using brute strength and a large weapon, which have the same weakness Sora exploited when facing Saïx.

Battle Quotes

 * "Can you feel it? The moon's power?"
 * "Moon, shine down!"
 * "Begone!"
 * "DIE!"
 * "Fool..."
 * "I misjudged you..."
 * "No excuses"
 * "You want to see me die fighting?"
 * "Move aside!"
 * "All shall be lost to you!"
 * "A heart... if I had a heart..."

Trivia

 * In the Japanese version, Saïx was voiced by seiyuu Ginpei Sato, who voiced a Before Crisis Turk that made a cameo in Last Order. In the English version, Saïx, was voiced by anime VA Kirk Thornton, who voiced Ed of Brave Fencer Musashi. This would be the 2nd time the two VAs would voice the same character, the first being Jin of Samurai Champloo, who is similarly stoic to Saïx but lacks a berserker side.
 * Why he is second in command when he is number VII is unknown. Possibly because he was the first of the new members that were not former apprentices to Ansem, or that the number seven is, in mathematical terms, the median (number that marks the center) of the list of numbers from 1 to 13. Another possibility is that the ranking system of the Organization is not a representation of superiority, but rather is simply an indication of when the member joined (this is likely, as Marluxia, the lowly-ranked number XI, was made Lord of Castle Oblivion in Chain of Memories). Also, he might have been the strongest member next to Xemnas. Xemnas probably felt he was the most reliable member. Another reason, though hugely unlikely, is that it was an homage to Final Fantasy VII, arguably the most popular game of the Final Fantasy Series.
 * Saïx's name is pronounced 'Sigh-ax' in the English version of the game. The katakana suggests that the pronounciation is actually the same as 'Sykes', however.