Yes...I know. You wouldn't do that. But...I was jealous.
~ Saix admitting to Lea he let his jealousy get the better of him when referring to his friendship with Roxas and Xion
Humanity is a precious gift. And yet you desire to return to the Organization?
~ Saix to Vexen
Saïx, the Luna Diviner, is one of the secondary antagonists in the Kingdom Hearts series. He is the seventh member of the original Organization XIII and a member of the new Organization. He wields a claymore and the power of the Moon, using the latter to enter a berserk rage. He commands the Berserker nobodies. He is the Nobody of Isa who is Lea's best friend.
Despite being an antagonist however, Saïx (alongside Demyx) served as an anti-hero in Kingdom Hearts III although he was apart of Xehanort thirteen seekers of darkness he secretly plotted against him as he seeked to atone for his past misdeeds as he was the driving force of bringing Roxas and Xion back despite mistreating them while in Organization XIII as well as make amends with his best friend Lea. He met Even (Vexen's somebody) to recruit him back into Organization to gain access to the replica program to find a way to bring Roxas, Xion and Naminé indirectly helping Lea in his ultimate goal of brining his friends back, the latter seeking to atone as well agrees and later recruits Demyx to help them in their plot against Xehanort, as a result he indirectly protects Lea and Xion from getting killed by Xemnas in the final battle by having Roxas rescue them in time.
He is voiced by Ginpei Sato in Japanese, and by Kirk Thornton in English, who also voiced Kevin Ryman of the Outbreak Survivors in Resident Evil: Outbreak.
Saïx plays a relatively important role in Organization XIII, assigning missions to all the other Organization members. Saïx is the one who gave Xemnas's orders to Axel to eliminate traitors to their Organization 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 stood in the way of their plans, such as Vexen and Zexion. Saïx is also revealed to be the one who picked which members would be going to Castle Oblivion, namely the members suspected of being traitors, as well as anyone else who was "getting in the way". Those who fell victim to this plot were Marluxia (who attempted to take control of the Organization for himself by manipulating Sora through Namine) Larxene (who co-conspired with Marluxia), Zexion, Vexen and Lexaeus (the latter three who countered Marluxia's plot by using the Riku Replica).
After Axel's return from Castle Oblivion and his growing friendship with Roxas and Xion, a rift between Saïx and Axel begins to form. He eventually confronts Axel of this, as their friendship is more concrete because their original selves were best friends. Eventually, Saïx dismisses his previous plans with Axel as "just an idle fantasy", as they both have changed too much for them to be friends anymore.
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. Saïx 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, hooded 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 resurrect Xion. While not confronting Roxas himself, it is possible that Saïx was the one who sent the Neoshadows after Roxas, who destroys the Heartless easily.
Kingdom Hearts II
Saïx's first appearance is in Hollow Bastion, along with all surviving and loyal Organization members to taunt Sora.
Saïx first appears in the Sandlot after Sora and company rescue Seifer from lesser Nobodies. Saïx appears before the trio, applauding their battle skills. He informs them of a traitor, Axel, and believes 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 ends 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.
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 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. Then 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).
The World That Never Was
Saïx is seen again talking to Kairi in her cell in the Castle That Never Was within the world of Nobodies. 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, her Nobody, 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 on their escape. Saïx soon appears and attempts to stop Kairi and Naminé, but Riku (still cloaked and in the form of Xehanort's Heartless) attacks him from behind. Saïx does a backflip 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 with and he can now safely be killed. Saïx smiles savagely 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 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 Saïx's great strength, speed, power, and skill, 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
Kingdom Hearts III
Following the Organization's failure to turn Sora into a vessel, Master Xehanort, Xigbar, and Saïx meet at the Keyblade Graveyard to find a way to complete the Organization. Saïx, having discovered Vexen's notes on the forgotten Xion, suggests using her to replace Sora, and decides to fetch Vexen to refine the replicas. Visiting Radiant Garden, Saïx approaches Even, who is wandering the square, with an offer to rejoin the Organization. At the Keyblade Graveyard, Vexen lies that he chose to return to the Organization to continue research on his Replica Program, with Saïx saying Ansem did not appreciate his abilities while Xehanort did. Saïx would the begin to work with Vexen to atone for his past misdeeds against Roxas and Axel.
Saïx later appears at the Clock Tower in Twilight Town with Lea, but with no intention of fighting him. The two talk as if they were still friends, their conversation revealing their true motives for joining the original Organization XIII; as Somebodies, they had befriended a girl only referred to as Subject X, who was held inside the castle of Radiant Garden. When she disappeared, the two became apprentices of Ansem the Wise before he too disappeared and Isa became a Nobody alongside Lea. Their entire reason for climbing the ranks of Organization XIII was to get information on Subject X and learn what happened to her, knowing full well that Xemnas, as Xehanort's Nobody, has knowledge of her predicament, but they had no luck in finding her. Saïx's anger at Axel's newfound friendship with Roxas and Xion was out of betrayal, feeling Axel had decided to forget about Subject X. Lea rebuffs, trying to persuade Saïx to leave the new Organization, but Saïx retorts by saying Roxas is gone forever too. Saïx and Lea part ways fully expecting to battle one another at the fated place.
Later, Saïx and Xion confront Kairi and Lea at the Keyblade Graveyard, with Saïx subtly trying to jog Xion's memories by calling Lea, "Axel" several times, however when Saïx mentions Roxas it causes her to attack Lea and Kairi before Sora's arrival. Saïx overpowers Lea, who once again tries to persuade his old friend to stop, until Xemnas arrives and berates Lea for his treason. Saïx simply watches as Xemnas mercilessly attacks both Lea and Xion before Roxas arrives to save them. Xemnas kidnaps Kairi, leaving Saïx to deal with their enemies. Sora, Roxas, and Xion fight and defeat Saïx. When Lea approaches Saïx, the latter asks why he looks sad. Lea responds by commenting on what the Organization has reduced Saïx to. Saïx once again reminds Lea of his betrayal, not to the Organization, but to him, as he befriended Roxas and Xion while abandoning their goals after everything Saïx had done to try and find her. Lea assures him he never forgot, which Saïx knew deep down, allowing his jealousy to get the better of him. He fades away in Lea's arms, being called by his real name before being reborn as his original self.
Through a Secret Report, it was revealed he was actually a key part of the Guardians of Lights' victory; having met Even, both expressed a desire to atone for their past actions. Since Saïx was already in the real Organization XIII, he had the ability to bring Even in as a Nobody once again, the latter willing to sacrifice his new life to get access to his Replica Program, which would allow Roxas, Xion, and Naminé to become human and therefore coexist with their original selves. Interestingly, by doing this he (and Vexen) indirectly assisted in Lea in achieving his goal of finding a way to bring his friends back.
Sometime after in the game's epilogue Isa is reborn as his original self and reunites with Lea, Roxas and Xion on top of Twilight Tower hands out sea-salt ice cream and are joined by Hayner, Pence and Olette and together they join the others at Destiny Islands for a celebration, Isa and the others bear witness to Sora and Kairi reuniting one last time before the former disappears for misusing the power of waking.
Vexen and Saïx meet each other before plotting against Xehanort for their atonement.
"Got it Memorized?"
Saix slowly attempting to jog Xion's memories.
Saix continues to jog Xion's memories by mentionioning Roxas and Axel.
Saïx admitting to Lea he was jealous of Lea's friendship with Roxas and Xion
Saïx bidding farewell to Lea before being reborn as Isa.
Isa finally reborn and redeemed becomes friends with Roxas and Xion.