Zexion (ゼクシオン, Zekushion?) is also known as the "Cloaked Schemer" (影歩む策士, Kage Ayumu Sakushi?, lit. "Shadow-walking Schemer") and he uses his power of illusion to mimic others' weapons, disguise himself as others, and create duplicates of himself.[4] He uses a lexicon, "Book of Retribution" (裁きの書, Sabaki no Sho?), as his weapon. He was originally Ienzo (イエンツォ, Ientso?), a silent young boy adopted by Ansem after his parents passed away for unknown reasons. He would then become Ansem's apprentice, meeting Ven while he was attacked by the Unversed, and suggested the creation of an underground lab for their research on the heart. Prior to Kingdom Hearts II Final Mix, Zexion's weapon and powers were not revealed because Nomura was unsure if it would be revealed later. Nomura decided to keep it a secret and the development team depicted the character's gravestone in the World That Never Was that would have shown his weapon as destroyed.[1] The character's voice actors are Akira Ishida for the Japanese game releases and Vince Corazza for the English releases.[13][25]

Zexion makes a minor appearance in 358/2 Days, training Roxas before he leaves for Castle Oblivion. Zexion is one of two Organization members who only appear in Riku's story mode in Chain of Memories. Originally, Zexion had planned to use Riku against Marluxia and his co-conspirators. After Sora defeats the Riku Replica and Marluxia, however, Zexion sees Riku to be of no use and attempts to destroy him.[37] Using the card Axel created from Sora's memories, Zexion draws Riku into a simulation of Destiny Islands where he torments the Riku with his guilt over the islands being destroyed. He then assumes the guise of Sora and attacks Riku, telling him that he's become a pawn for the darkness. He engulfs Riku in light, but Naminé (disguised as Kairi) intervenes to convince Riku to accept both darkness and light. With newfound confidence, Riku overpowers Zexion, causing him to retreat. Afterward, Axel brings the Riku Replica to Zexion, convincing the replica that he can become "real" by gaining power that the real Riku does not have.[38] The replica agrees and kills Zexion to take his power as his own. It is later revealed that Zexion's death wasn't due to betrayal, but rather that he "knew too much".[38]