Vexen, the "Chilly Academic"(The Freezing Achedemic Japan), is a stoic scientist who appears in Kingdom Hearts: Chain of Memories. His original self was Even and he was interested in studying Xehanort's memories. Vexen can control ice and carries a large shield in battle that blocks any frontal attacks made against him. Vexen is voiced by Tatsuya Kando in Kingdom Hearts: Chain of Memories and Nachi Nozawa in Kingdom Hearts Re: Chain of Memories.

Vexen sides with Zexion and Lexaeus, other high-ranked members occupying the castle's basements, to prevent Marluxia from using Sora to overthrow the Organization. He first battles Riku in order to gather data to create a replica of him. However, Vexen cares nothing for his "experiment" and allows Naminé to manipulate the Riku Replica's memories against his wishes. When he encounters Sora, Vexen says that he came to collect his "debt" and provokes Sora's anger by making him believe that he controlled Riku rather than created a replica. After their battle, Vexen gives Sora the card to Twilight Town with the intention of revealing Roxas's existence. Marluxia considers him a traitor as a result and sends Axel to kill him.

In Twilight Town, Vexen attempts to reveal to Sora why he feels as though he has been to Twilight Town despite being fairly certain that he had never been there. Sora and Vexen battle again after Vexen tells Sora to throw away his memories and listen to his heart. After being defeated, Vexen sees Sora as a true threat; even after being weakened by false memories, Sora remained very strong. As Vexen is about to reveal Marluxia's plot and Roxas's existence, Vexen is killed by Axel.

Chain of Memories Manga and KHII: Final Mix[]

In the Chain of Memories manga, Vexen is portrayed as a buffoonish character, constantly upset with the lack of respect he receives from the younger members. He is in association with Lexaeus and Zexion in the underground of Castle Oblivion, all three switching mundane chores such as "cooking", "comms" and "patrol". He produces a set of Vexen Replicas that leave Castle Oblivion along with the Riku Replica in a humorous short.In Kingdom Hearts II Final Mix, Vexen is shown in a flashback sequence asking Zexion where Xemnas is while Xemnas is occupied with the female Keyblade wielder's armor