Vexen

How Vexen joined the Tourney
Vexen plays a relatively minor role in Kingdom Hearts 358/2 Days, but it should be noted that this role plays a major contribution to the game's central plot. Adviser and leader of the Castle Oblivion-based Replica Program that created Xion, he was present when the replica joined Organization XIII. Vexen then was assigned on Day 12 to teach Roxas the art of reconnaissance in Twilight Town, and was later sent away to Castle Oblivion, where he used his Replica Program to create the Riku Replica in order to challenge Sora.

Vexen was later exterminated by Axel to earn Marluxia's trust and for the purpose of raising Saïx through the ranks. All Vexen had left behind after his demise was knowledge that Axel later discovered in a document Vexen had composed about Naminé in the Castle That Never Was's library. This Nobody's only other mention in Kingdom Hearts 358/2 Days was when Xemnas revealed the truth about Xion before the surviving members of Organization XIII in Where Nothing Gathers.

In Kingdom Hearts: Chain of Memories, Vexen has parts in both Sora's and Riku's storylines. He assists Lexaeus and Zexion in their efforts to stop Marluxia (whom Vexen loathed) and Larxene (whom he was not too fond of either) from overthrowing the Organization (Axel, the other Organization member residing in the castle, is deemed too unpredictable to be anything other than a liability). To do this, Vexen and his cohorts intend to use Riku's darkness to counteract Sora's light.

Vexen engages Riku in a cautious battle and uses the data he obtained from the fight to create a copy of Riku that lacks a heart. The replica is completely aware of his status as a fake, but unlike Riku, is not afraid to use the darkness. However, even with darkness on his side, the replica fails to defeat Riku.

Even with the failure, Vexen has other plans for the replica, and goes to Marluxia and Larxene. He offers the replica to test Sora, though first he would have to have his memories changed around. They then have Naminé manipulate the replica's memories until he thinks he is the real Riku. He also believes that he made a promise to Naminé like Sora had, and because of this conflict, the replica confronts Sora multiple times, saying that Naminé no longer needs Sora.

Though Larxene and Axel also make brief appearances in the cutscenes of Reverse/Rebirth, Vexen is the only Organization XIII member in Chain of Memories who is fought as a boss in both Sora and Riku's stories. In Riku's story, Vexen confronts Riku on a mission to gain data on Riku without him noticing. When the battle is over, Vexen reveals his true objective and reminds Riku of the Darkness inside him. Vexen flees, taunting Riku. It is later revealed that the "data" Vexen received from this battle is what created the Riku Replica. Vexen is never seen again in Riku's story, but it is mentioned by Axel and Lexaeus later on that he has indeed been slain.

However, they soon lose control of the replica, and Marluxia deems Vexen's experiment a failure. Vexen is insulted, saying that a novice like Marluxia has no right to speak to an elder like himself. However, when Marluxia makes the threat of reporting Vexen's failure to "the Superior", Vexen's fear of the Superior's power overrides his previous elitist attitude. Now with Vexen under his grip, Marluxia manages to persuade Vexen to eliminate Sora.

Vexen then confronts Sora, saying that Sora is in debt to him for reuniting him with Riku. Sora is angered, and the two battle. However, as they fight, Vexen delves deep into Sora's heart, and creates a world card forged from the memories in the other side of his heart. Vexen tells Sora that if he wants to truly defeat him, then he must enter that world.

Meanwhile, Marluxia, Larxene, and Axel note that Vexen is jeopardizing their plans, for if Sora discovers the other side of his heart, then he will no longer be of any use to them. They then send Axel to eliminate Vexen during his battle with Sora, before Vexen tells Sora of their plan.

Sora discovers that the new world is Twilight Town, which is strange because Sora has only visited places in his memories, and he has no memories of Twilight Town. Even so, Sora feels a sense of familiarity from this place. He explores the town until he arrives at the gates of a mansion. Vexen makes his appearance there, asking Sora if the familiarity of this place or his memories of Naminé are true. Sora doesn't understand what he means, and Vexen sees that he is but a slave of his memories, just like "his Riku". Sora is again angered, and battles Vexen one more time.

Vexen is defeated again, and after seeing that Sora is too dangerous and powerful, plans to tell him of Marluxia's plot and, by extension, Roxas's existence. Before he can fully explain, Axel appears and strikes Vexen with one of his chakrams and embeds it into Vexen's body. When Vexen asks why he'd attacked him, Axel explains that he will eliminate Vexen and tells him that he can be "nothing instead of just being a Nobody". Vexen begs to be spared, but Axel replies with a heartless "goodbye" and snaps his fingers, detonating the chakram and incinerating Vexen, making him the first member of Organization XIII to fade out of existence.

Resurrected years later, Vexen hopes to guide a former Espada named Luppi Antenor down the path Sosuke Aizen went, when he was resurrected by Mayuri.

When highlighted
Holds his shield Frozen Pride near his lab notes.

After the announcer calls his name
Pierces Frozen Pride forward and the camera zooms and raises an icicle saying "I'm a scientist. Experiments are what I do, yes."

Blizzara (Neutral)
Vexen sends a homing ice shard at his opponent.

Freeze (Side)
Vexen focuses his power on the opponent saying "I shall freeze you!" encasing the prey in ice and coming in close to attack, dealing additional damage.

Tundra Shard (Up)
Vexen creates an icicle on Frozen Pride and jumps into the air slashing upwards with the icicle.

Ice Burn (Down)
Vexen creates pools of slippery ice on the ground that hinders the opponent's movements.

Diamond Dust (Hyper Smash)
Vexen spreads his arms saying "I've had enough of this!" then three large mounds of ice that ascend from the ground to strike enemies, dealing ice damage and freezing enemies. These mounds last five times.

Slide Break (Final Smash)
Vexen elongates the bottom of the Frozen Pride saying "Come to me, ice blade.", transforming it into a monstrous ice blade. He then slashes the with the empowered weapon numerous times before performing a downward slam "Away you go!", thus shattering the ice blade and reverting his Shield to normal.

Victory Animations

 * 1) Vexen raises Frozen Pride and summons an icicle near him saying "Accept me as your master, experiment!"
 * 2) Vexen cuts a lab note in half and says "You're too much trouble!"
 * 3) Vexen sends ice shards out of Frozen Pride and says "I told you I would make good use of you, didn't I?"

On-Screen Appearance
Vexen appears in an iceburg and cuts it open, then says "I see no need to tell you. Why trouble in your final moments?"

Trivia

 * Vexen's rival is the former replacing Sexta Espada, Luppi Antenor.
 * Vexen shares his English voice actor with Uryu Ishida, Yoichi Hiruma, Kazuki Kazama and Eddie, the Forbidden Beast.
 * Vexen shares his French voice actor with Lu Su, Kraken Isaac, Cao Cao and Col. Nick Alexander.
 * Vexen shares his German voice actor with Kano.
 * Vexen shares his Arabic voice actor with Wilbur.
 * Vexen shares his Mandarin Chinese voice actor with Hurt Plant, Gru and[ [King Lukas]].