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.
- 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 preserves. Additionally, twelve replicas were created from the chosen Thirteen Seekers of Darkness (aside from Master Xehanort).
- Demyx - A member of the old Organization.
- As revealed in the Kingdom Hearts III Ultimania, the Thirteen Seekers of Darkness were original meant to have ranks like Organization XIII, but was changed in order to help avoid confusion with characters that had previous ranks in the original Organization.
- Members that were known to have ranks prior to this change were Master Xehanort as Rank I, Xemnas as Rank II, Ansem as Rank III, Xigbar as Rank IV, Saix as Rank VII, Young Xehanort as Rank XII, and Xion as Rank XIII.