The Thirteen Seekers of Darkness (13人の闇の探求者 Jūsannin no Yami no Tankyūsha?), also known as the Real Organization XIII (真のXIII機関 Shin no Jūsan Kikan?), is a group consisting of thirteen different incarnations of Master Xehanort that debuts in Kingdom Hearts 3D: Dream Drop Distance. The main goal of the group is to clash against the Seven Guardians of Light at the Keyblade Graveyard in order to forge the χ-blade, a weapon that would allow its user to open Kingdom Hearts. They serve as the main antagonists of Kingdom Hearts 3D: Dream Drop Distance and Kingdom Hearts III.
The actual purpose of the original Organization XIII was to host a fragment of Xehanort's heart in each member, turning them into his vessels, therefore replicating the thirteen pieces of darkness that emerged from the shattered χ-blade. However, many of the original members turned out to be either too weak or traitorous, leaving only Xigbar and Saïx as worthy members. However, Master Xehanort managed to gather 12 vessels of himself thanks to Young Xehanort and Ansem, Seeker of Darkness, though he failed to make Sora the last one, and fled with an incomplete Organization to put his plan in practice. Yen Sid has already told Mickey about this in Signs of What's Next, when he said that one Keyblade Master alone will not be enough to face what is "not a single Xehanort".
Before Kingdom Hearts 3D: Dream Drop Distance
Master Xehanort's goal was to provoke a second Keyblade War to obtain the all-powerful χ-blade. For this, he first tried to confront a heart of pure darkness and a heart of pure light. However, since Master Xehanort was a man of foresight, he prepared a contingency plan that would allow him, in the event of failure of the first plan, to reach his final goal anyway. For this reason, he placed a part of his heart in Braig, one of the guards of the Radiant Garden, knowing that he would always be faithful to him and then made this man one of his receptacles. He also managed to place another fragment of his heart inside another keyblade holder and made it his second receptacle. After taking possession of Terra's body, Terra-Xehanort became Xehanort, the amnesic apprentice found by Ansem the Wise.
While conducting experiments on the nature of the human heart with the other Ansem disciples, Xehanort found his memories of yesteryear and knew that, to achieve his goal, he would have to gather and confront thirteen hearts of pure darkness and seven hearts of pure light. When Xehanort and the other apprentices opened their hearts to Darkness, they turned into Heartless and Nobodies.
Ansem, Seeker of Darkness was thus tasked with bringing together the seven Princesses of Heart. For that, he manipulated Maleficent by making him believe that reuniting the Princesses would allow him to access Kingdom Hearts, which would allow him to control all the worlds.
Meanwhile, Xemnas, Xehanort's Nobody, formed the Organization XIII, composed of thirteen Nobodies. The real purpose of Xemnas was to reunite these thirteen Nobodies, lead them to Kingdom Hearts to make them the thirteen receptacles of Master Xehanort's Darkness.
However, during his early adventures, Sora put an end to the Heartless and Nobody's plans by eliminating both of them and destroying Organization XIII.
When Sora arrived at the World That Never Was, he was arrested by Xigbar and Xemnas who with the Young Xehanort, explained to him that thanks to Sora, they realized that most of the members originally chosen to become receptacles of Master Xehanort were not adequate, since their hearts were not fit to receive that of Master Xehanort. Since then he had replaced them with other receptacles. However, he had only twelve. Sora fell asleep in the darkness when he learned that he was supposed to become the thirteenth and last receptacle.
After defeating Ansem, Riku arrived in the Round Room of the Castle That Never Was. There he found Sora, asleep on one of the thirteen seats. As he rushed to his friend, Riku was thrown by the Young Xehanort who forbade him to get his "new receptacle". In the face of Riku's misunderstanding, Xehanort explained that most of the original members of Organization XIII were ultimately not adequate to become receptacles of Master Xehanort. They had to replace them. While they first thought of Riku as the last receptacle, they realized that Riku had developed some resistance to Darkness. They then took Sora replacing. Then the True Organization XIII appeared under the astonished eyes of Riku. At that moment, King Mickey arrived and saved the latter from Young Xehanort. However, he resisted the fate of the king and confronted Riku. After his defeat, Xehanort canceled Mickey's spell and everyone attended Master Xehanort's comeback.
The latter then explained to them that despite several failed attempts to forge the Χ-blade, the clash of the Thirteen Dark Seekers against the Seven Guardians of Light would suddenly lead to the creation of the legendary χ-blade. While Master Xehanort was preparing to place a fragment of his heart inside Sora, his last receptacle, the latter was saved in extremis by Lea. The members of the Organization disappeared thereafter; each member returning to his true time.
The Seeker are present through out the story, each one goading the Guardians to fight them in one way or another. They eventually meet up at the Keyblade Graveyard and are eventually all destroyed.
- Master Xehanort - Original incarnation of Xehanort, a Keyblade Master who masterminded behind all the chaos and destruction that has besieged the Realm of Light thus far.
- Attribute: Darkness.
- Weapon: Keyblade (The Gazing Eye).
- Xemnas - Master Xehanort's Nobody. He created the original Organization XIII, however Sora and Riku, as well as internal strife quickly reduced their numbers. Sora and Riku destroyed him, causing him to fade away into nothingness, however due to Young Xehanort's meddling in time he has returned.
- Ansem, Seeker of Darkness - Master Xehanort's Heartless. His missions were to both enable Xehanort's younger self to travel through time and oversee Maleficent gather the seven Princesses of Heart. Though he possessed Riku to regain physical form to go after Kingdom Hearts, Sora put an end to his plans. His Darkness lingered within Riku until the boy put an end to him, however he has been revived due to Young Xehanort's travels through time.
- Young Xehanort - Younger version of the original Xehanort. Meeting Ansem, Xehanort was enable to journey through time as an insurance plan in case he and Xemnas failed on their own. It is due to him that the True Organization XIII was able to rise.
- Attributes: Darkness and Time.
- Weapons: Unnamed Keyblade and unnamed Etheareal Blades.
- Xigbar - Nobody of Braig, a mercenary hired by Master Xehanort to help speed Terra's descent into Darkness, Xigbar was Xemnas's right hand in the original Organization XIII, however Sora put an end to him. Despite this he has returned due to Young Xehanort's interference. He reveals that he joined Xehanort so he could claim the power of the Keyblade as his own, although it is revealed later that he had another reason.
- Saïx - Nobody of Isa, and Xemnas' second in command of the old Organization XIII. His reasons for becoming a member of the True Organization XIII are because he believed that his friend from when they were human, Lea/Axel, had forgotten about him and grew jealous when he made other friends. Sora ended him once before, however due to Young Xehanort he has returned.
- Vanitas - Embodiment of the darkness of Ventus' heart created by Master Xehanort. Due to Ventus being connected to Sora's heart, Vanitas is connected to Sora too.
- Larxene - Nobody of Elrena and member of the old Organization who tried to take it over alongside Marluxia.
- Luxord - Member of the old Organization. Original persona unknown.
- Marluxia - Nobody of Lauriam and member of the old Organization who tried to take over it.
- Dark Riku - Replica of Riku is used as one of the Seekers of Darkness.
- Attribute: Darkness.
- Weapon: Sword (Replica Soul Eater).
- Terra-Xehanort - The body of Terra possessed by Xehanort's heart.
- Xion - An unofficial member of the old Organization, now used by Xehanort in order to fill up a spot in the new Organization XIII.
In case any of the Thirteen Seekers became unavailable, Master Xehanort also set aside two spare members as reserves. Additionally, twelve replicas were created from the chosen Thirteen Seekers of Darkness (aside from Master Xehanort).
- Demyx - A member of the old Organization.
By the end of Kingdom Hearts III, the Thirteen Seekers of Darkness were defunct, with some eliminated, some returning to their own time and some being re-completed into their original selves.
All members will be presented here in order of the end of their time as a chosen seeker of darkness:
- Dark Riku - Dark Riku was defeated by Sora, Riku and Riku Replica, the final blow being carried by Riku Replica. It was discovered that Dark Riku was not the real Riku from the time when Ansem had taken possession of his body, but the Riku Replica from the time Naminé had reconstituted his memory so that he thinks he is the real Riku. With that, the heart of Dark Riku returned to its rightful place in the timeline, and his body went on to serve as a vessel for the heart of Naminé.
- Xigbar - Xigbar was defeated by Sora and Riku. It was later discovered that he merely simulated his elimination to be able to recover the Gazing Eye, as well as the Black Box, and fulfill his role as Luxu. It is unknown if he returned to being Braig or if he has remained as Xigbar.
- Luxord - Luxord was eliminated by Sora. Before disappearing, he will give a "wild card" to Sora so that it "turns the tables". It is not yet known whether he was re-completed.
- Larxene - Larxene was eliminated by Sora and Mickey. She admitted that she had followed Marluxia in both Organizations XIII in order to repay her "debt" to him. It is not yet known whether she was re-completed to become Elrena again.
- Marluxia - Marluxia was eliminated by Sora and Mickey. Before disappearing, he thanks Sora for returning the memories of his old life. It is not yet known whether he was recompleted to become Lauriam again.
- Vanitas - Vanitas was defeated by Sora, Ventus and Aqua. Vanitas declared himself satisfied with the role he had plays as a shadow cast by the light of his "brothers". With that, the heart of Vanitas returned to its place and time of origin.
- Terra-Xehanort - Terra-Xehanort was temporarily neutralized by Sora, Ventus and Aqua before the defeat of Vanitas, then completely defeated by Sora and the Guardian, who turned out to be Terra's Heartless. With that, the heart of Terra-Xehanort was returned to its original time, and the real Terra reclaimed his body to become an additional Guardian of Light.
- Xion - As she was about to "finish" Lea on Xemnas' orders, Roxas will temporarily take possession of Sora's body to prevent her, and, by uttering her once forgotten name, will return her all his old memories. Xion will then find her place in the memories of her friends, especially Lea, and will become an additional Guardian of Light while the heart of her past self that had inhabited the replica body found its place in its time of origin.
- Saïx - Saïx was eliminated by Sora, Roxas and Xion. He admitted the reasons for his actions: he wanted first to find the girl called "Subject X" who served as guinea pig for the Ansem the Wise and Xehanort's experiments, but had finally succumbed to jealousy when Axel had become attached to Roxas and Xion. He was finally reconstituted to become Isa again.
- Ansem - Ansem was defeated by Sora, Riku and Mickey. He recognized Riku's true strength over the power of darkness, and as a Keyblade Master. Thus, Ansem's heart will return to its original era.
- Xemnas - Xemnas was defeated by Sora, Riku, and Mickey. Regaining his emotions, he reflected on the painful loneliness of the loss of his comrades, but ended up recognizing, thanks to Sora, that pain serves to remind humans that they are living. Thus, Xemnas' heart will return to its original era.
- Young Xehanort - Young Xehanort was defeated by Sora, Riku and Mickey. He taunts Sora on the dangers of the Power of Waking one last time before vanishing. Thus, Young Xehanort's heart will return to its original era.
- Master Xehanort - Master Xehanort and his twelve Replicas were defeated by Sora, Donald and Goofy. Nevertheless, the old Keyblade Master admits his defeat thanks to Master Eraqus, then a refugee inside Terra. Xehanort then hands over the χ-blade to Sora and finally joins Kingdom Hearts alongside Eraqus.
- As revealed in the Kingdom Hearts III Ultimania, members of the Thirteen Seekers of Darkness were originally meant to be ranked like their counterparts in the original Organization. This was changed in order to avoid confusion between ranked characters of either group.