Castle Oblivion

Castle Oblivion (忘却の城) is an In-Between Realm world which appears in Kingdom Hearts: Chain of Memories, and is the only real world in the game. It is controlled by Marluxia of Organization XIII, and consists of thirteen floors and twelve basements.

Organization Headquarters
The history of Castle Oblivion before Chain of Memories is still unclear, but it is known that it was eventually found by Xemnas of Organization XIII, who decided to convert it into a new headquarters for the Organization. It was intended to be a place to research memories, an important topic to the Nobodies of the Organization, who have only their memories to form personalities with. Xemnas sent Xigbar and Xaldin to recruit more members for the Organization, as they needed a large group in order to run the castle. Eventually, a strange Nobody named Naminé appeared in the castle and was found by the Organization. She soon became the center of their research, due to her strange abilities of memory manipulation. In order to further research, Xemnas also developed pods that could be used to piece together memories. The castle and Naminé were then entrusted to the neophyte Marluxia, but he would soon plot to use this power in a bid to seize control over the Organization. While Marluxia, and his associates Larxene and Axel controlled the top half of the castle, the senior members Vexen, Lexaeus, and Zexion controlled the basements. Throughout their appearances, they are shown to have a strong rivalry.

In Kingdom Hearts II Final Mix, Xigbar and Zexion discussed the new Castle and the Chamber of Repose which Xemnas constructed while he was Xehanort, and which he frequently went to. Xigbar believed that Xemnas was looking for the complementary Chamber of Waking, and that this place might be somewhere in Castle Oblivion.

Kingdom Hearts Birth by Sleep
In a recent trailer for the upcoming prequel, Aqua is seen standing in front of Castle Oblivion. Terra is also seen running from a flood of water, which appears to be in a Castle Oblivion hallway.

Kingdom Hearts: Chain of Memories
After defeating Ansem and restoring the damaged worlds, Sora, Donald Duck, and Goofy find themselves in a grassy field with the King's dog, Pluto. They follow Pluto along the path to Castle Oblivion, and as soon as they enter the castle, they forget all of their skills and are forced to rely upon the castle's memory-based card system. Though Marluxia and the other Organization members tell them their memory loss is simply the nature of the castle, it is revealed that the mysterious girl Naminé is actually the one reshaping Sora's memories, so that Marluxia and Larxene can use him as a puppet warrior against Xemnas. The scheme fails thanks to the meddling of Axel, and Marluxia and Larxene are lost to the darkness at Sora's hand. Sora then uses one of Xemnas' pods so that Naminé can restore his memories, and is eventually moved to Twilight Town.

Meanwhile, Sora's friend Riku awakens from the darkness within the lowest basement of Castle Oblivion, where he faces his memories of Maleficent and the remaining darkness of Ansem. Though he initially sets out to destroy the indelible darkness in his heart, with the help of DiZ, Naminé, and King Mickey, he is able to eventually embrace both the light and the dark, achieving balance. The three basement members, Vexen, Lexaeus, and Zexion seek to recruit Riku in order to counter Marluxia's use of Sora, but Riku denies their requests and vanquishes them. Riku eventually defeats the Ansem in his heart, and decides not to have Naminé seal it away completely by erasing his memories; instead he sets out on the "road to dawn" in order to help while Sora is sleeping.

Kingdom Hearts 358/2 Days
On the 22nd Day to Roxas's existence, about half of the Organization members are sent to Castle Oblivion, a castle in the world between worlds. The Organization found it and is using it as a research facility. Lexaeus, Zexion, Marluxia and Larxene are sent first, and the next day Axel and Vexen join them. The Hero of the Keyblade, Sora, arrives there at about the same time, and the Organization, using a special girl called Naminé, tamper with his Memories. Several days later Riku, Sora's best friend, arrives there as well, giving Vexen the perfect opportunity to gather data of him and create a replica of Riku. Due to the members going up against Sora and Riku, as well as inner conflicts between their ranks, they fall one by one, starting with Vexen. A month later, the only member of the Organization still alive is Axel – who is responsible personally for both Vexen and Zexion's deaths. Day 49 marks Sora's "falling asleep" in order to restore his Memories. On Day 52 Axel is left alone in the castle and turns to tend to one more task handed down to him by Saix aside from eliminating the traitors to the Organization. The mission is to search for the Chamber of Waking, a place of interest for Xemnas no one else knows much about. He will leave there on Day 71 – empty handed, and from Day 118 to 149 will be dispatched there yet again, still to find only nothing.

Day 255 marks Axel's third venture into Castle Oblivion on a mission, where he stumbles upon Xion who came there on a search of her own. Simply setting foot in the Castle makes Xion collapse as Memories flow into her. She recalls being there with Saix, who told her she will not see Castle Oblivion again before ushering her out. When Axel shows up, he finds Xion on her knees. She's surprised to see him but he offers her a cold front. He hasn't a clue what the girl hoped to find in such an empty place. Xion snaps at him – that is the place she came from, and all of the answers she seeks are there. As though he failed to hear her, Axel asks Xion about her mission for the day, implying she shouldn't be there. If she disobeys orders, the Organization will destroy her. The girl asks if it's because she's useless but Axel protests – he never said that. He tells her to go home, but Xion can't. She's remembering things about who she used to be. Axel tells her in return to stop remembering; nothing good will come of it. She claims to remember Axel, however, and to make matters worse she insists they met right there – in Castle Oblivion. Axel refuses to heed her words, making Xion stomp her foot down and plead for him to help her. She needs to know who she was, and with that final declaration she simply runs away. Axel calls after her, telling her not to go further. He can't stop her though and she steps past a door into a bright white light. There, she manages to view her Memories, but it's hardly what she expected to see – She is not the same person she was before becoming a Nobody.

Axel and Roxas come to the castle over a month later on yet another mission. No sooner does Roxas step into the castle, however, he falls to the ground as images begin to fill his mind. Axel insists they retreat but Roxas refuses. If he hangs on just a bit more, sees one more picture… yet before he manages to see anything of any worth, he passes out, and Axel drags him out of there through a Corridor of Darkness.

Kingdom Hearts II
The outside of Castle Oblivion was briefly shown in Roxas's final dreams, as Sora's memories end as he opens the door. The Castle's inside was only seen in the opening credits, Sora's battle with Marluxia, Riku's battle with Ansem, Naminé's placing Sora in the Memory Pod, as well as several other important events in Kingdom Hearts: Chain of Memories illustrated in full computer graphics.

Trivia

 * The need for the card system in Castle Oblivion is unknown. Though Marluxia claims that they are simply part of the castle, he claims that the trademark memory loss was due to the castle's influence as well, when in actuality it was Naminé's doing. It is possible that the card system was created by the Organization simply to disorient and manipulate intruders like Riku and Sora.

Gallery
Manoir Oblivion