Majority of information taken from The Keyhole-Saïx.
Saïx, the Luna Diviner (月に舞う魔人, Tsuki ni Mau Majin, lit. Demoniac Dancing in the Moon), is the Nobody of Isa, Rank VII within Organization XIII, as well as the second-in-command, and next to Xemnas, the main antagonist in both Kingdom Hearts II and Kingdom Hearts 358/2 Days. He derives power from the Moon, and uses this power to enter a berserk rage where he mercilessly attacks opponents with his massive claymore. He commands the Berserker Nobodies. Fittingly, Saïx is the second-to-last member of the Organization to fall. Along with all other Organization members in Kingdom Hearts 358/2 Days, Saïx is a playable character in Mission Mode.
Saïx wears a basic Organization black coat along with the usual black gloves and boots. He has long, frayed blue hair framing his face, though slicked back in wild spikes at the top. Behind, it reaches down to his mid-back and is cut slightly neater. A distinctive trait of Saïx's is the X-shaped scar between his yellow eyes that extends to about halfway up his forehead in one direction and to just under his eyes in the other. When Saïx enters his "Berserk" state, his eyes turn completely yellow, his scar becomes more jagged and a bit larger, and his hair becomes much messier. No matter what state, he wears a single studded earring on each pointed ear.
Saïx's transformation under the moon's power is a possible reference to several things, including: the ancient belief that the moon caused madness, hence the term "lunatic"; the modern belief that the phases of the moon can affect a person's mood; the legend of the werewolf, humans who became savage beasts under the influence of a full moon; as well as the berserker warriors of the Norse, who wore clothes made from bear skins as they went into battle in an insane fury and are the source of the modern term "berserk".
Next to Xemnas, Saïx appears to be one of the most "Nobody-like" of the Organization. Despite claiming to remember what possessing a heart was like, he behaves mostly as a cold, emotionless, and efficient operative until his final battle. In almost all of his appearances, Saïx acts very calmly, never losing composure in even the direst of situations. He is very aware of how emotions are unreal to them, unlike other members who imitate their emotions. He instead uses his memories of a heart to cruelly manipulate the hearts and behavior of others. He coldly toyed with Sora's emotions by having him beg to see Kairi, only to refuse his request. Saïx also sent the "useless" members to their deaths at Castle Oblivion under the guise of Xemnas's orders for the sake of his and Axel's plans. This was a smart tactic to simultaneously move up his rank while eliminating any competition or rebellion.
However, in Kingdom Hearts 358/2 Days it seems he still values his friendship with Axel from their time as humans over that which Axel has formed with Xion and Roxas, as was confirmed in the Secret Reports. From this it seems he believes that Nobodies cannot form a real friendship without having had one with another beforehand, thus having memories to fall back on. He couldn't care less about Xion as a person and views her as only a tool for their needs. Literally, Saïx views her as a puppet, and even insists that the others say "it" when referring to Xion rather than "she". This sort of callous behavior is what caused the friendship between Axel and himself to weaken, though Saïx couldn't understand why Axel (and Roxas) concerned himself with her. He changed too much after becoming a Nobody, according to Axel, leading to Axel's ignoring him for Roxas and Xion. Thus, Saïx has a much colder demeanor towards Axel when they meet in Hollow Bastion after Axel has run astray despite their past connection.
The only thing Saïx seems to "care" about in the end is acquiring a heart and, by extension, Kingdom Hearts. He will do all he can to attain it, even turning on fellow allies without hesitation when they become obstacles, as happened with Axel. His near-obsessive devotion to his goal is his undoing. Throughout the game he repeatedly states his desire to "truly, finally exist", and it turns out his last words are only to Kingdom Hearts, sadly asking for his heart.
However this doesn't make him blind to Xemnas' plans for Kingdom Hearts, which differ from his own, as he had originally plotted with Axel to overthrow Xemnas. Unlike Marluxia, this was only to regain his and Axel's hearts. Without Axel, he likely went along with Xemnas' plans since it was the most convenient action. Xemnas had a seemingly surefire way of granting what Saïx desired, even if he didn't intend to grant it. Saïx was careful enough to skillfully play "charades", devoted to Kingdom Hearts, but not necessarily Xemnas, who was a means to an unfortunate end.
Further still, his usual calm and goal-oriented demeanor belies a fierce savagery. In his final confrontation with Sora under the heart-shaped moon of Kingdom Hearts, Saïx becomes a berserk force of destruction. Unlike his reserved manner that is usual of him, he roars, shouts, and attacks relentlessly in battle with no sense of self-control. In fact, Saïx is practically psychotic under the influence of Kingdom Hearts. What this raging state says of Saïx's own emotional capacity is unclear if it's not merely a manifestation of Kingdom Hearts' absorbed power.
Saïx is a powerful member of Organization XIII and a capable fighter. Although he appears calm and collected throughout when speaking, in battle he becomes a wild, dangerous opponent. He uses brute strength and his large Claymore to attack, but his true danger is his "Berserk" form, which uses the power of the moon. A "Berserk" gauge in the top of the screen measures how close he is to becoming berserk. When it fills, Saïx's Lunatic Claymore shifts shape and produces a white aura which serves as extra blades. Saïx himself grows bestial, with glowing eyes, manic hair, and bared fangs. His strength and speed increase greatly, and he will rapidly slam his Claymore into the ground, producing shockwaves. When he swings or throws the Claymore, it will leave a wake of blue flames.
However, Sora can pick up any of the Claymores that Saïx releases, allowing him to use Reaction Commands that will knock Saïx out of his berserk state, as well as inflicting significant damage. When knocked out of his berserk state, Saïx will spend most of his time with his arms stretched towards the moon, absorbing its power.
The Nobodies under his command, the Berserkers, follow his attack style, using brute strength and a large weapon, but share the same weakness as Saïx.
In Kingdom Hearts 358/2 Days, Saïx's Limit Break is also called Berserk. During Berserk, Saïx goes into a berserk stage; he rushes across the field, dealing continuous, devastating damage to enemies that he comes down hitting with his claymore. When the attack button is pressed, he will jump and perform a stronger smashing attack. Each smashing attack is followed up by a shockwave.
During Saïx's Final Limit, Saïx goes into an even more berserk stage; He comes down to attack even more often, and exerts a sphere of his strength straight from himself while in the air before coming down. The shockwaves that come after each attack also increase in range.
Saïx wields a massive blade known as a Claymore. His signature Claymore is known as Lunatic. Despite many dissimilarities to real claymores, Saïx does use a very large, two-handed bladed weapon. His Claymore is decorated with many additives that resemble the Nobody logo, in blues and yellows. When in normal form, Saïx attacks with powerful slashes and combos with the bladed edges.
Although it seems to be a completely different weapon, the Cursed Hammer of the Berserker Nobodies is used in much the same way, and even has the same Reaction Command.
The names of Saïx's various claymores are all references to astronomy or astrology (especially the moon), with the exceptions of Crocea Mors (Latin for "yellow death") in the Japanese version, which is the purported name of Julius Caesar's sword; and Just Desserts, his joke weapon.
Kingdom Hearts Birth by Sleep
- Main article: Isa
Kingdom Hearts 358/2 Days
Saïx plays a relatively important role in Kingdom Hearts 358/2 Days. He assigns Roxas his missions in The Grey Area at the Castle That Never Was, and is present when Xion joins the Organization. He remains in this station throughout the beginning and middle of the game.
Saïx is the one who gave Xemnas's orders to Axel to rid Organization XIII of the traitors in Castle Oblivion. It is generally accepted by the remaining members that at this point the two planned to not only eliminate traitors, but also anyone who got in the way of their plan, such as Vexen and Zexion.
After Axel's return from Castle Oblivion and the growing friendship between Axel, Roxas and Xion, a rift between Saïx and Axel begins to form. He eventually confronts Axel, revealing the Nobody's past, along with his true name. By the time of Roxas's departure from the Organization, Saïx dismisses his previous plans with Axel as "just an idle fantasy", as both have changed.
Working on Organization XIII's plans for Sora with Xemnas, he later challenges Roxas to a battle of will when the Keyblade wielder attempts to leave Organization XIII. He loses the battle, and Roxas escapes. Up until Xion's destruction and absorption at the hands of Roxas, Saïx views the Sora copy as nothing but a mere puppet. He even insists that the others would say "it" when referring to Xion, rather than "she".
After Xion's end, Xemnas orders Saïx to retrieve Roxas, who is on his way to the Castle That Never Was to defeat Organization XIII and free Kingdom Hearts, because he believes it will bring Xion back. While not confronting Roxas himself, it is possible that Saïx was the one who sent the Neoshadows after Roxas, who destroyed the Heartless easily.
Kingdom Hearts II
Saïx's first appearance is in Hollow Bastion, along with the surviving Organization members, excluding Axel, to taunt Sora. He remarks "You're doing well", but like the others (except for Xigbar), does not confront Sora, and simply stands next to Xemnas.
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 declares he is not worried, prompting Saïx to remark that the Organization would want nothing to happen to Sora. He also cryptically remarks that the Organization knows how to "injure a heart". He then opens a portal of darkness 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 succeeded in placing Sora in a state of confusion and frustration to keep him going toward their goal. Saïx also states that Axel may prove a thorn in their side, which leads to Xemnas giving him orders to deal with the renegade.
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 is not mollified, his only goal being to enter the realm of darkness to rescue Kairi. His face unreadable, Saïx asks Sora to prove just how much he cares about Kairi. In response, Sora actually gets onto his knees and begs at the Nobody's feet. Seeing Sora's devotion to the Princess of Heart, Saïx sees this as a further opportunity to enrage and confuse Sora so that he might further the Organization's goal. He refuses Sora's wish, eliciting a hot fury. Bending Sora's anger to suit his own needs, Saïx convinces Sora to destroy more Heartless so that the hearts held within them are released by the Keyblade, so that they may flock to Xemnas' synthetic Kingdom Hearts, which will be all the closer to completion because of it.
At that moment, Maleficent appears, declaring with much aplomb 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 places herself between Sora and the Nobodies, telling him to devise a way to vanquish the Organization. Swarmed by Nobodies, she is overwhelmed and disappears, allowing Saïx to resume convincing Sora to release more hearts. But before he can finish his ploy, Sora, Donald, and Goofy are rescued by a portal of darkness that swallows them up (which was Maleficent's doing).
Saïx is seen again talking to Kairi in her cell in the Castle That Never Was. He tells her, much to her horror, that she is the "fire that feeds Sora's anger." Kairi realizes that Sora is getting lured into a trap all because of her. However, Naminé unexpectedly appears in her cell, and rescues her through a portal of darkness. The two halves then begin fleeing the castle to try and make good their escape. Saïx soon appears and attempts to stop Kairi and Naminé, but Riku, still cloaked and in the form of Ansem, Seeker of Darkness, attacks him from behind. Saïx does a back flip in the air, and lands a few feet away. Riku slams him up against the wall, intending to finish him once and for all. However, Saïx opens up a portal behind him and sinks away into the wall with a smirk.
Saïx again appears in the Castle That Never Was to Sora, who had managed to work his way through the Organization's floating fortress with the help of Donald, Goofy, Riku, and Kairi. He looks lovingly upon his Kingdom Hearts, his source of power. He tells Sora 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 the Organization's Kingdom Hearts is nearly done, pointing to the heart-shaped moon in the sky. He then enigmatically asks Sora if he can hear the euphoria of the countless hearts he has harvested. He 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, wondering in an amused voice if the intrusions will ever end, 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 this "charade," and Xemnas grants him permission. Sora's part in their plan is done, he has given them every heart required, and he can now safely be killed. Saïx smiles savagely and remarks that he's waited so long to hear that.
Elsewhere in the castle, after Luxord's defeat, 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 have made it this far, though Donald vehemently states that he is Sora. Saïx seems not to care, simply stating: "Different name, same fate." Then, summoning his claymore, he creates a potent shockwave with sheer strength alone. This power manages to push away Kairi and Riku back towards the entrance of the room. He then quickly erects a force field, separating them from the battle, yet doing no harm. Them taken care of, he confronts Sora, Donald, and Goofy for the final time. He finally lets his outer decorum slip away. Under the influence of the moon, he becomes savage and unrestrained, truly a model for his Berserker Nobodies.
However, despite the incredible power and abilities he drew from the moon of Kingdom Hearts, he is overcome. Defeated and mortally wounded, he limps away from Sora to the ledge overlooking the moon. With the last of his strength, he asks: "Why...Kingdom Hearts...Where is my heart?" All his power gone, he now fades back into darkness. Sora watches with a brief look of pity and regret, then turns to rejoin Kairi and Riku.
Day 9: On Track
Xion is being monitored. Roxas, meanwhile, has begun his training exercises. It is imperative we keep Xion from having undue contact with Roxas until we are certain it will perform as expected - which will take another 10 days, if Vexen's convictions are to be trusted. As for the Keyblade Master, Marluxia will no doubt be keeping an eye on him.
Day 51: Measures Must Be Taken
The Replica Program continues apace, but something has gone wrong at Castle Oblivion. The Dusks returned with word that none of those we dispatched survived - but the news came in fragments. I still know too little to extract the truth. I doubt Axel would be among those lost, but I must plan for the worst. First, I must locate the Keyblade master.
Day 94: All Goes Apace
The hearts collected by our two Keyblade wielders, Roxas and Xion, have gathered together; and now, almighty Kingdom Hearts waxes large in the night sky. Our efforts have come to bear fruit, nearly ripe for the plucking. All plans proceed smoothly - alarmingly so, in fact, though this is no time to be deterred by paranoia.
Day 150: Dealing with Xion
As expected, the Duplicate is starting to show its limits. The Program showed promise, but a puppet is just a puppet: something to be toyed with until it breaks. I am utterly at a loss as to what Roxas and Axel see in that thing. How best to dispose of it merits my consideration going forward.
Day 171: The No. i Project
Xion failed to complete its mission. If this continues, destroying it and using the next Replica as the Duplicate would undoubtedly yield a higher-grade copy. No. i was among the initial lot, which naturally raises questions about its capabilities. At present, it is nothing short of broken. I cannot fathom why Xemnas would want to keep it.
Day 174: Just a Replica
Xion continues to sleep. All analysis on its function suggests no marked change. The copying appears to be working, but a Replica is a Replica. My latest report to Xemnas on this net me no clear answers. He simply stood, smiling. At times I find his thinking impenetrable.
Day 277: True Agenda
Axel and Roxas are up to something. No plot they concoct will change the fact that the Organization has cast off Xion, though. Our plans have split, diverged, and advance now to the next stage. The No. i project and Replica Program merely paved the way. Our true goals lie elsewhere.
Day 298: Change of Plans
Axel failed to report that the impostor and Xion are working together. Instead, that news came from Roxas. The boy is far more easily handled than Axel, but now Axel has captured Xion and returned her to us. His motives are impossible to read. Our plans can be altered if necessary, but doing so can only delay their realization.
Day 356: Unforeseen Events
Our plans never accounted for the possibility of both Xion and Roxas leaving. How did this come to pass? When did Roxas grow strong enough to outmuscle me? What were you really after, Lea? We joined the Organization at the same time, and formulated our plan. At this point, it's just an idle fantasy. Everything changed. You, and me.