Axel, the Flurry of Dancing Flames. Axel is the eighth member of Organization XIII, and is considered to be a wild card by the other members of the Organization. He acted as a double agent during the events in Castle Oblivion (which occurred during Kingdom Hearts: Chain of Memories), keeping track of Marluxia's plans (he planned to overthrow the Organization) and would then later go on to betray the Organization when he refused to kill his old friend Roxas. Axel has the ability to control fire and wields red and silver chakrams, often combining his ability to weild them with his ability to control fire to create powerful attacks. He controls the lesser Nobody known as 'Assassin Nobodies'.
Lea ( the human form of Axel) along with Isa (Saix's human form) are seen in a cut scene half way through Ventus campaign in Kingdom Hearts Birth By Sleep in Radiant Garden. The teenage Lea indroduces, adds his catch phrase "Got it memorized?" and challeges Ventus to a practice fight. After Lea is beaten embarrassingly Isa tells Lea they have to go and part ways with newly befriended Ventus. Lea and Isa are last seen asking each other if they are ready and looking at the castle in Radiant Garden.
Axel makes his first appearance in Kingdom Hearts: Chain of Memories. While Sora progresses from the ground floor up to the top of the castle and Riku progresses from the basement up, Axel works for both divided parts of the Organization. On one side of this divide were Larxene and Marluxia, who planned to manipulate Sora to help them overthrow the Organization, and on the other side was Vexen, Laxaeus and Zexion, three of the original members of the Organization who knew of Marluxia's plan and planned on using Riku to defeat Sora, should Marluxia succeed in his plan to use Sora to eliminate other Organization members. Axel, though his intentions are still unclear, joins the rebel group - at first.
Early in the game Axel fights Sora to test him and Sora proves to be worthy foe. Axel happily gives Sora a card that allows him to progress further into the castle. Not long after, we see Axel telling Larxene that he is very intrigued in Sora because he retained his self-consciousness after becoming a Heartless.
After Vexen nearly reveals to Sora the existence of Roxas, Axel is ordered by Marluxia to dispose of Vexen, and does so (rather effortlessly at that), and gains the trust of Marluxia and Larxene in the process. Using this new found trust to his advantage by allowing Namine to escape and contact Sora (Namine was being held by Marluxia and used to change and remove Sora's memories). Later on Axel confronts Marluxia, finally revealing himself to be a double agent, citing his previous order was to rid the Organization of traitors. Axel prepares to attack, but Marluxia uses Namine to shield himself. Axel, being a Nobody without a conscious, resolves to go through Namine to get him, but is interrupted by Sora, who he battles. Axel pretends to be defeated, and attempts to (and successfully does so) confuse Sora by saying "I don't deserve this after I helped you..." and vanishes, pretending to fade away.
Axel then meets with Zexion, who discusses Riku and requests data on Destiny Islands. Despite the two working together on this matter, Axel later manipulates the Riku Replica into killing Zexion,
promising him that he would gain new powers and be able to defeat the real Riku, and become "real" himself. Axel justifies his betrayal by saying Sora and Riku's future will be more interesting to watch than to save Zexion, although it is more likely that he did it to protect Sora (because of his friendship with Roxas), as if Zexion succeeded in making Riku give into his darkness, it may have harmed Sora (and therefore potentially affect Roxas). It is found out in 358/2 days from his and Saix's reports, that despite being sent to Castle Oblivion to deal with the betrayers his personal goal was to have every organisation member there killed, so that he and Saix ( who was his friend before they became nobodies ) could at some point take control of the organisation for themselves ( probably after killing everyone else as well ). However as time passes he befriends Roxas and his relationship with Saix turns sour this plan gets abandoned. This is probably the reason Saix is the second in command of the Organisation aswell.
In between Kingdom Hearts: Chain of Memories and Kingdom Hearts II, Roxas (Sora's Nobody) is plagued with question relating to the Keyblade and wants to seek out Sora, and to do so, leaves
the Organization. Axel, who found a rare friendship in Roxas, was distraught by his decision. Roxas would go on to be captured by Riku and put in Ansem the Wise's Digital Twilight Town where his memory was completely wiped out and replaced with artificial intelligence and memory, making him believe himself to be an average teenager. Once the Organization located this town, Axel was sent there to bring Roxas back to the Organization. Roxas, who has no memories whatsoever, is dumbfounded by Axel's appearance and comments and has no idea of what is actually going on. Axel is forced to accept the Organization's order to either eliminate Roxas (due to his unwillingness to return) or be destroyed himself. Axel tries once more to recover Roxas without killing him, and Roxas beginning to remember him gives him hope, but he is frozen in place by Ansem (who controls everything within Twilight Town). The two meet again for the last time, when Roxas remembers Axel, but Axel says its too late and is forced to fight Roxas. Axel, perhaps not truly able to battle to full potential against a former friend, was defeated and disappears, choosing not to carry out his mission, and as such becomes branded a traitor. Meanwhile Roxas merges with Sora once again, and Axel was entrusted with Namine by Riku.
While Sora and co. were exploring various worlds, Axel appears before Kairi, hoping that once he kidnaps her, he will draw out Sora and be able to turn him into a Heartless (thus making a Nobody, which would mean Roxas would return). However, Kairi escapes through a corridor of darkness created by Riku, leading her to Twilight Town where she waited for Sora. However, Axel returns to kidnap her once more, but she is taken captive by Saix instead, who hopes to enrage Sora, causing him to kill more Heartless and fill up Kingdom Hearts.
After Sora's battle with the Heatless Army in Hollow Bastion, Sora confronts Xemnas (the leader of the Organization), who decides to take his leave. Axel then appears and greets Sora, hinting that the keyblade causes the hearts that composed the heartless to leave them, but refuses to say what the Organization plans to do with the hearts. He also apologizes for losing Kairi, but immediately flees when Saix appears on the scene. (should Saix catch Axel, the Organization would then turn Axel into a dusk for failing to capture Roxas).
Axel's next appearance would be his last in the game, as he meets Sora on the way to The World that Never Was when Sora finds himself trapped in Betwixt and Between by Nobodies. Axel arrives to help and battles the Nobodies with Sora, but the numbers soon become too overwhelming, and Axel performs a kamikaze-like attack, destroying all the Nobodies in the process. As his body begins to fade, Axel uses his last strength to open the passageway to The World that Never was. As he dies, he once again apologizes for involving Kairi, but justifies himself by saying that Roxas made him feel like he had a heart, and that Sora makes him feel the same way.
Tetsuya Nomura has confirmed that Axel will be a playable character in the upcoming DS title "Kingdom Hearts 358/2 Days". As the game explores Roxas' time with the Organization, it can be assumed that Axel, as Roxas' best friend, will be a big component to the story.