Vexen is a Nobody known as the "Chilly Academic" . Vexen's original self was Even , and he was interested in studying Xehanort's memories. Vexen can control ice and carries a large shield called "Frozen Pride" in battle. The character first appeared in Kingdom Hearts: Chain of Memories, where Tatsuya Kando provided the voice for simple battle expressions. Vexen was included as an optional boss in the Japanese exclusive Kingdom Hearts II Final Mix, and was voiced by Nachi Nozawa. Nozawa returned to provide voice acting for dialogue in the re-release of Chain of Memories and Kingdom Hearts 358/2 Days. Vexen's English voice acting was done by Derek Stephen Prince.
In Chain of Memories, Vexen sides with Zexion and Lexaeus, other members occupying the castle's basements, to prevent Marluxia's plan to overthrow the Organization. He battles Riku in order to gather data to create a replica of him, and is later assigned to investigate Marluxia's intentions. Vexen allows Naminé to manipulate the Riku Replica's memories to test Sora's worth. When the Replica fails to defeat Sora, Marluxia threatens to reveal the shortcoming to Xemnas, forcing Vexen to fight Sora himself in an attempt to kill the boy. After their battle, Vexen gives Sora the card to access Twilight Town in Castle Oblivion with the intention of revealing Roxas's existence. As a result, Marluxia considers him a traitor and sends Axel to kill him. In Twilight Town, Vexen attempts to reveal to Sora why Twilight Town feels familiar to him. Vexen battles Sora again, but is killed by Axel as he is about to reveal Marluxia's plot.