Zexion is number VI in Organization XIII and is also known as The Cloaked Schemer, his weapon is a 3-4ft book that's pretty thick
(please log in to view the image)
Zexion has the ability to identify individuals by their scent and is able to sense when they die by noticing their scents fading, and seems to be able to do so from great distances. His power is over illusion, used to mimic others' weapons, disguise himself as others, and create duplicates of himself. His unique weapon is a lexicon; with it, he is able to send out a flurry of pages to attack the opponent and trap them into the pages.
History:
[SPOILER - highlight to read]: Zexion informs Vexen and Lexaeus that he senses a scent "exactly similar" to that of Xemnas and identified as Riku. Riku's actions are tracked until Vexen's death, when Zexion and Lexaeus decide to use Riku to counter Marluxia's plan to use Sora. After Marluxia is killed, Zexion sees Riku as unnecessary and attempts to destroy Riku himself. He does not plan to use brute force, because of personal preference and the fact that Riku was able to defeat the powerful Lexaeus. He leads Riku into a manifestation of Destiny Islands, Riku's home. There, Zexion tells Riku about how he threw away his friends and his home and opened the door to darkness, thus destroying the islands.
Following Riku's battle with a large Heartless, Zexion disguises himself as Sora and attacks Riku, telling him that he's become a pawn of the darkness. He engulfs Riku in light, but a vision of Kairi (who is actually Naminé in disguise) convinces Riku to accept darkness and light. With newfound confidence, Riku follows Zexion's scent through the light and strikes him; Zexion flees. Axel brings the Riku Replica to Zexion and convinces the replica that he can become "real" by gaining power that the real Riku does not have. The replica agrees, and as per Axel's suggestion, kills Zexion.
Power Abilities
Zexion has the power of illusion. He can create copies of himself, along with the ability change his appearance and the appearance of a location. He can trap his enemies in his book, wherein They are attacked by books that hit extremely hard, or cut by the papers should you destroy one, you may only escape by destroy a clone of Zexion, which the books make impossible. He can hover off the floor and by doing so can move at a great speed. He can attack with a kind of smoke screen then throw his book at you. When he gets more serious he can trap you in his books in his book and play with you, if you fail his little game you will be struck by meteors.