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 the original Organization XIII and a member of the real Organization XIII. 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.
In the original Organization, Saïx serves as the second-in-command to Xemnas, and is the secondary antagonist of Kingdom Hearts II and Kingdom Hearts 358/2 Days. Fittingly, Saïx is the second-to-last member of the first Organization to fall. Along with all other original Organization members in Kingdom Hearts 358/2 Days, Saïx is a playable character in Mission Mode.
Before Kingdom Hearts 358/2 Days
Saïx joins the Organization with Axel, believing that Xemnas would know what happened to their friend Subject X. To this end, Saïx works to get as close to Xemnas as possible while Axel secretly assists him to further their goal.
Kingdom Hearts 358/2 Days
Saïx assigns missions to the other Organization members. Along with Xemnas, Xigbar and Vexen, he also oversees the Replica Program. When Roxas is brought into the Organization as its thirteenth member, Saïx suggests he keep a diary.
After Sora defeats Ansem, Seeker of Darkness, Saïx sends Marluxia, Larxene, Vexen, Lexaeus, Zexion, and Axel to Castle Oblivion, intending for Axel to eliminate the members who planned to betray the Organization.
Over time, Roxas and Xion's friendship with Axel creates tension between Saïx and Axel. Saïx grows frustrated with Xion's declining performance as she struggles to wield the Keyblade, as well as with Axel's attachment to her.
With Roxas getting weaker from Xion sapping his strength, Saïx plans for them to fight to the death, as the Organization only needs one Keyblade wielder. He sends them separately to Halloween Town, secretly causing both to see the other as an Orcus. However, Axel intervenes and snaps them out of the spell.
When Roxas leaves the Organization, Saïx attempts to stop him, but is defeated.
After Xion's demise, Xemnas orders Saïx to retrieve Roxas.
Kingdom Hearts II
Saïx appears with the rest of the surviving Organization members to taunt Sora at Hollow Bastion. When the Organization discusses their plans for Sora, Saïx expresses his doubts on Sora's usefulness and states that those who have lost their "true purpose" will inevitably destroy themselves.
Saïx later manages to track Axel down and take Kairi from him as a hostage for the Organization.
Saïx confronts Sora upon Sora's second visit to Twilight Town, leaving him confused and frustrated. Saïx warns Sora that Axel has betrayed the Organization and is attempting to turn Sora into a Heartless.
During the Battle of the 1000 Heartless, Saïx appears while Axel is telling Sora about the Organization's plans, forcing Axel to flee. Sora pleads with Saïx to take him to Kairi. Saïx refuses, and tells Sora to destroy more Heartless to continue building Kingdom Hearts. Maleficent appears, declaring Kingdom Hearts will belong to her. She summons Soldiers to attack, but Saïx has Dusks destroy them. After the Nobodies overwhelm Maleficent, Saïx summons more Heartless and departs through a corridor of darkness.
In the Castle That Never Was, Saïx watches over Kairi in her cell, telling her that she is "the fire that feeds Sora's anger". When Naminé rescues Kairi through a corridor of darkness, Saïx appears to prevent their escape. Riku, still cloaked and in the form of Ansem, Seeker of Darkness, comes to Kairi's aid and attacks Saïx, who retreats through a corridor of darkness.
Saïx appears to Sora in the Hall of Empty Melodies. He tells Sora that Kairi no longer needs him as a "friend from the darkness" is with her. Saïx summons more Heartless for Sora to destroy before leaving. Saïx then appears to Xemnas, who is watching Kingdom Hearts come closer to completion, and asks if he can end the "charade," to which Xemnas agrees.
Elsewhere in the castle, after Luxord's defeat, Saïx awaits Sora, Donald, Goofy, Riku, and Kairi in the Addled Impasse. He calls Sora by Roxas's name and declares that the two of them will share the same fate before creating a shockwave that pushes Kairi and Riku back. Saïx confronts Sora, Donald, and Goofy, but is defeated. In his last moments, he reaches for Kingdom Hearts, asking it where his own heart is before fading away.
Kingdom Hearts 3D: Dream Drop Distance
Upon being reborn as Isa, Saïx is taken by Braig and Young Xehanort to be made a part of the real Organization XIII. Wanting to atone for his mistreatment of Axel and Roxas, Isa agrees to rejoin the group and becomes Saïx again to house a fragment of Master Xehanort's heart. While collecting five of the six near-perfected replicas left behind by Vexen in order to house the time traveling hearts of Ansem, Xemnas, Young Xehanort, Vanitas, and Dark Riku, Saix finds Vexen's records on the replica project and the forgotten prototype No. i, sparking his memory of Xion.
When Xehanort's attempt to make Sora his final vessel ends in failure due to Lea's intervention, Saïx attacks Lea, revealing his identity. After Donald and Goofy arrive, the real Organization XIII retreat to await the time to properly forge the χ-blade.
Kingdom Hearts III
After the replicas proved unable to hold time traveling hearts indefinitely, Saïx retreats to the Keyblade Graveyard with Master Xehanort and Xigbar. After confirming the status of the other members, Saïx suggests using Xion to take the thirteenth slot, deeming Vexen and Demyx "backups". He then leaves to recruit Vexen.
Saïx visits Even in Radiant Garden's central square and offers him the chance to atone for his past actions as Vexen through the replicas. Even accepts and returns to his Nobody form. Together, Saïx and Vexen work secretly to provide replicas for "those who truly deserve them". Later meeting at the Keyblade Graveyard, Vexen updates Saïx on his progress with perfecting the replicas, telling him they will be able to become real people once they're given hearts.
In Twilight Town, Saïx meets with Lea on the Clock Tower. The two recount their original intent of rescuing Subject X before joining the Organization. Saïx tells Lea that Roxas is gone, just like Subject X, to which Lea declares that he will find a way to save all of his friends, including Saïx.
In the Keyblade Graveyard, Lea and Kairi pair up to fight Saïx and Xion. Sora soon joins them but Saïx overpowers them. As Saïx rushes towards Sora and Kairi, Lea steps in to defend them but is pushed back. Xemnas appears and condemns Lea for his traitorous actions. Saïx watches silently as Xemnas attacks and injures Lea as well as Xion before Roxas appears and comes to their rescue.
Xemnas proceeds to kidnap Kairi and leaves the group to fight the berserk Saïx. Xion and Roxas aid Sora in battling Saïx as Lea is too injured to fight. When the battle concludes, Lea rushes over to Saïx. Saïx admits his feelings of jealousy towards Lea's friendships with Roxas and Xion and reconciles with Lea before fading away.
Kingdom Hearts Union χ[Cross]
Saïx appears as an enemy in the July 2018 NEW XIII Event.
Super Smash Bros. Ultimate
Saïx wears a basic Organization black coat, along with the usual black gloves and boots. He has long blue hair vaguely reminiscent of Vexen's in style and length, though Saïx's is a bit wilder at the top. Most of his hair is tucked into his cloak, though a portion is not and falls over the back. As a vessel for Xehanort's heart, Saïx shares his pointed ears and amber eyes, as does his fellow vessel Xigbar. Saïx also wears stud earrings like Xaldin's. The X-shaped scar on Saïx's face is his most distinctive trait, with the vertex of this "X" lying between his eyes and extending from halfway up his forehead to just under his eyes. When Saïx enters his "Berserk" state, his eyes turn completely yellow, his scar becomes more jagged and a bit larger, and his hair becomes spiky and unruly.
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 bearskins as they went into battle in an insane fury and are the source of the modern term "berserk."
A slightly-modified copy of Saïx's body model is used for Young Xehanort's in Kingdom Hearts Birth by Sleep, though it is likely that this is simply due to data recycling rather than any deeper significance.
Along with 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, even in the direst of situations. He is very aware of how emotions are unreal to them, unlike other members who imitate their emotions. However, in Kingdom Hearts 358/2 Days, it seems he values his friendship with Axel from their time as humans, indicating that he believes that Nobodies cannot even try to genuinely show emotion or form a real friendship without having had one with another beforehand, thus having memories to fall back on. According to Axel, the friendship between them weakened due to how Saïx changed too much after becoming a Nobody, leading to Axel ignoring him for Roxas and Xion.Thus, Saïx has a colder demeanor towards Axel in Kingdom Hearts II.
Saïx would later admit that his cold treatment of Axel was due to him being jealous of Axel's friendship with Roxas and Xion after Axel seemingly forgot about him and their goal of finding the girl; though Saïx would later admit that he knew better and that his old friend would never forget nor abandon him.
The only thing Saïx seems to "care" about is acquiring a heart and, by extension, Kingdom Hearts. More than any other member of the Organization, Saïx is portrayed the most dedicated to their goal, repeatedly stating his desire to "truly, finally exist". Even his last words were to Kingdom Hearts, sadly asking for his heart. Though this doesn't make him blind to Xemnas's plans to use Kingdom Hearts for more power, as he had originally plotted with Axel to overthrow Xemnas to regain their hearts. Saïx can also be quite cruel, claiming to know very well how to injure a heart. He had a keen insight into manipulating others, such as when he toyed with Sora's emotions by having him beg to see Kairi, only to refuse his request. He also sent the "useless" members to Castle Oblivion under the guise of Xemnas's orders to clear the way for his and Axel's plans, moving up the ranks while eliminating any competition or rebellion.
However, his usual calm exterior belies a more savage nature. In his final confrontation with Sora under the heart-shaped moon of Kingdom Hearts, he becomes a berserk force of destruction. Unlike his calm and reserved manner, in battle, he roars, shouts, and attacks relentlessly with no sense of self-control and portrays a psychotic behavior under the influence of Kingdom Hearts.
Kingdom Hearts III has Saïx show a more sympathetic and remorseful side. Seeking redemption and forgiveness for his treatment of Roxas and Xion and a desire to rekindle his friendship with Axel, Saïx infiltrates the real Organization and ensures the guardians of light are given access to the replicas to save the two. He eventually becomes friends with Roxas and Xion after he returned to his human self. Saix is also good at being subtle, trying to jog Xion's memories by using the names of her friends Axel and Roxas without drawing Xemnas's suspicion.
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. As proof of his power, in Kingdom Hearts III, Saïx was capable of overpowering Sora and Kairi while in his Berserk form and would have easily finished both, including Lea and the renegade Xion if Roxas hadn't come to aid them in the confrontation. A "Berserk" gauge at 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 that serves as extra blades. Saïx himself grows bestial, with glowing eyes, manic hair, and bared fangs. Saïx's 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 enters a berserk stage; he rushes across the field and causes shockwaves. This intensifies during the Final Limit.
In Kingdom Hearts III, Saix is shown to draw upon the limited moonlight at dusk. He also has access to a secondary "Berserk" guage, allowing him to create four additional claymores to attack with; he can use them as shields or a supply of makeshift projectiles.
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 Dichotomy's Japanese name, Crocea Mors (Latin for "yellow death"), which is the purported name of Julius Caesar's sword; and Just Desserts, his joke weapon.