Zexion

Zexion, the Cloaked Schemer (影歩む策士, Kageayumu Sakushi?, lit. Shadow-Walking Schemer), is the Nobody of Ienzo and is Rank VI in Organization XIII and an antagonist in Riku's storyline in Kingdom Hearts: Chain of Memories. He weaves illusions to fight for him. Unlike the other Organization members, Zexion's weapon was originally unknown, and his talents were used only outside of normal combat. In Kingdom Hearts Re:Chain of Memories, Zexion's weapon was revealed to be a book called a Lexicon.

Zexion appeared in Kingdom Hearts: Chain of Memories as a participant in the struggle within the Organization between the newer and veteran members. He is also central to the plot to use Riku as a puppet in Castle Oblivion. Zexion also appears in Kingdom Hearts 358/2 Days, as one of the playable characters in Mission Mode.

Between Kingdom Hearts Birth by Sleep and Kingdom Hearts 358/2 Days
Some time before Marluxia's official recruitment, Vexen tromped down the stairs of Twilight's View, calling out for Zexion and demanding to know where Xemnas was. Zexion answered that Xemnas was in the Chamber of Repose, and though Vexen complained, he decided to wait for Xemnas to return.

Xigbar was eavesdropping on the conversation, and dropped down after Vexen left. Zexion told him that he should continue his mission with Xaldin to recruit new members. After a short argument, Xigbar told Zexion that he had seen Xemnas, before they became Nobodies, conversing with someone in the underground labratory. Even though no one was supposed to be there, Xigbar believed that it could be his other "friend".

Kingdom Hearts 358/2 Days
Zexion is present when Xion joins Organization XIII. Zexion later teaches Roxas how to fill the mission gauge in Twilight Town before being sent away to Castle Oblivion. True to his personality, he was patient with the Keyblade wielder, carefully and calmly explaining the filling of the gauge in great detail.

After Axel returns from Castle Oblivion, Axel specifically mentions that he had eliminated Zexion, during a conversation with Saïx. Some time later, Axel admits that he doesn't mind "getting his hands dirty" to Saïx, and comments on killing both Zexion and Vexen.

During Xion's nightmare on Destiny Islands, Roxas stands on the beach of the island, missing his friend. He later sees the hooded Xion and approaches her. She removes her hood and turns out to be none other than Zexion, who proceeds to taunt a younger version of Riku as he did in Kingdom Hearts: Chain of Memories. The scene then begins to fade, Xion (in the form of the shocked Roxas) undergoing a series of transformations until she finally takes Sora's form for the first time.

Kingdom Hearts: Chain of Memories
After Sora had been lured into Castle Oblivion, Zexion discovers two other scents deep in the dungeons of the castle. One of them belongs to a Maleficent formed from someone's memory, having been given life by Castle Oblivion's unique properties. Originally, he mistakes the other scent to be that of "The Superior". Eventually, however, Zexion and his cohorts determine that the scent belongs to Riku, who had appeared in the Castle by force of will after Sora's arrival. Vexen hypothesizes that the darkness in Riku's heart, "Ansem", caused Zexion to mistake him for "the Superior", calling the effect "fascinating." Specifically, Riku's heart is plagued by the presence of Ansem.

Zexion, as well as Lexaeus and Vexen, come to see that Marluxia, keeper of Castle Oblivion, intends to take control of Organization XIII, with the help of Larxene, by using Sora as their puppet. Though they see that they can use Riku to counter Sora, they decide to oppose Marluxia's plot by having Vexen investigate Marluxia under the guise of offering to help using the Riku Replica he creates with combat data from the real Riku. However, Vexen is eventually killed on Marluxia's orders by Axel, whom Zexion and Lexaeus had been unsure about trusting. Axel later tells them he had performed the deed only to gain Marluxia's trust, and continues to cooperate with Zexion in tracking Sora and Riku.

Seeing that Vexen's efforts to derail Marluxia's plan had failed, Zexion sends Lexaeus to sway Riku into joining them, but Riku refuses to allow darkness to control him and defeats Lexaeus in combat. With the last of his strength, Lexaeus manages to knock Riku unconscious, rendering him helpless. However, before he can finish the job, Ansem takes control of Riku's body and finishes Lexaeus with the power of darkness. Riku is then enveloped in his own personal darkness, where "Ansem" tries to corrupt him - however, he is saved by King Mickey and continues ascending Castle Oblivion.

After Lexaeus dies in his failed attempt to subvert Riku's resistance to darkness, Zexion discusses the Organization's fate with Axel and learns that Larxene has been killed as well, bringing the number of Organization members eliminated to three. Axel tells him that he himself was defeated by Sora as well, and that Marluxia is almost certainly the next to go. Zexion decides that with the possibility of Marluxia dying soon, Riku is no longer needed, and heads off to intercept him.

Zexion appears before Riku while he is between floors of the castle, shortly after the death of Marluxia. As the force of Marluxia's death shakes the castle, Riku halts with surprise and comments how a very strong scent in the air has died. Zexion materializes in front of him and tells him that Sora has just defeated Marluxia. Riku is surprised to learn that Sora is also in the castle, but Zexion tells him he would never be able to face him after having such darkness in his heart.

He gives Riku a World Card to Destiny Islands, and Riku winds up facing a Darkside Heartless. After he defeats it, Zexion reappears, and continues to play on his guilt, telling him Sora will always oppose him as a host of the dark. Sora then appears himself, brandishing his Keyblade and accusing Riku of being corrupt. He envelops Riku in light, rendering him unable to do anything. Instead of drowning Riku into helplessness, however, the predicament causes Naminé to come to his aid, in the guise of Kairi, telling him that he should stop rejecting the darkness within his heart, and instead tells him to draw on that power to free himself of the oppressing light and strike out at Sora.

He wounds Sora, whose disguise falters to reveal Zexion, who had been using his powers of illusion to deceive Riku. Zexion is astounded by Riku's ability to control the darkness, and is also enraged at his perseverance. He decides to engage Riku in combat himself, albeit wounded, but still puts up a rather difficult fight. However, Riku eventually overcomes and defeats Zexion.

After escaping from Riku, Zexion appears in a room, where Axel and a companion are waiting. In a panic, Zexion thinks Axel's companion is Riku himself, but then realizes it's only Riku Replica. Axel and the replica then approach Zexion, and Axel directs the replica's attention to his lack of wholeness. He tells him that if he can find strength that the real Riku doesn't have, he can become a whole person of his own, rather than a mere puppet or whole copy of Riku.

Axel then suggests that he should start by eliminating Zexion. Zexion is horrified by Axel's suggestion, but before he can do anything, the replica eliminates Zexion and takes his power; judging by Axel's line of Zexion finding out "way too much", Axel having purposefully set this up in order to move Saïx up within the ranks of the Organization.