Roxas
Roxas is Sora's Nobody (his name is an anagram of Sora with the letter X added.) and the newest, not to mention youngest member of Organization XIII, and bears the title "Key of Destiny".
Birth
As said in the Secret Ansem Reports, Roxas was born when Sora stabbed himself with the Keyblade constructed from the hearts of six of the seven Princess of Heart in order to free Kairi's heart. However, this process also formed Kairi's Nobody, Naminé.
But Sora's time as a Heartless was short, as Kairi's light had fetched Sora's heart from the darkness, restoring him to his former self. Thus, Sora and Roxas co-existed, but Roxas would be without his true memories, and the two were incomplete without one another. Even so, Roxas' status as Sora's Nobody granted him the ability to use the Keyblade. This makes Roxas a very unusual Nobody.
Time in the Organization
Roxas, having been born in Twilight Town, was soon discovered by Xemnas, and was given his name. Having nowhere else to go, Roxas joined the Organization in hopes of finding the answers he needed.
During his stay, Roxas met Axel, and soon became the best friends. Even so, Roxas was growing increasingly impatient for the truth about himself, even as he used the Keyblade to bring the Organization closer to their goal of attaining Kingdom Hearts.
Eventually, Roxas was fed up, and left the Organization in order to find the answers, including the reason why he could use the Keyblade. Axel warned that the Organization would destroy him if he betrayed them, but Roxas was indifferent, and continued on, leaving a sad Axel behind.
Capture
Roxas, at one point, encountered Riku at Memory's Skyscraper, as countless Heartless surrounded him. The two fought off the Heartless together, but as soon as that threat was gone, they turned on each other. In the end, Roxas ended up the victor.
The next time however, Riku clad himself in darkness, taking on Xehanort's Heartless' form. With his newfound power, Riku was just barely able to bring back Roxas to the old mansion in Twilight Town, where DiZ resided. DiZ's intention was to join Sora and Roxas together, so that Sora may awaken and destroy the remaining members of the Organization. To do this, DiZ had Naminé get rid of Roxas' memories, and downloaded him into a digital Twilight Town, where he would remain completely unaware of his past life and his status as a Nobody.
Digital Twilight Town
For some time, Roxas lived a normal life in the digital Twilight Town, becoming best friends with three kids: Hayner, Pence, and Olette. It is this time in the digital Twilight Town that serves as the prologue to Kingdom Hearts II. But soon, he began experiencing mysterious dreams of Sora, and soon after mysterious events started to pop up around town. Strange white creatures, the Nobodies, kept coming and going, along with the Keyblade coming to his aid at opportune times. He also came into contact with the mysterious Naminé, which in turn brought him into mental contact with Kairi. He also encountered Riku, still in Xehanort's form, DiZ, and also scuffled with Axel, who tried getting Roxas to recall his memories. All of it made little sense to Roxas.
This all changed when summer vacation was coming to a close, and the truth came out: Roxas learned he was a Nobody, and that he was supposed to meet with Sora, the one from his dreams. Eventually, Roxas discovers that he was living in a digital Twilight Town, and that his friends weren't real. He once again encounters Axel, but DiZ manages to freeze Axel in his tracks, along with the rest of the world, save for Roxas, and told him to go to the haunted mansion. He does so, and there he encounters Naminé. As he makes his way through the mansion, Roxas begins to recall his former life, and in his rage, destroys Ansem's computer, though it is just a digital copy.
Roxas then encounters Axel one last time, but this time he is able to call on all of his dormant abilities, including summoning his two weapons: Oathkeeper and Oblivion, and soundly defeats his best friend, though sadly. He then enters the pod room, but not before seeing Donald and Goofy slumbering in their own pods. DiZ is there to greet him, revealing his intentions and fueling Roxas' rage with cutting remarks.
Roxas, in his anger, tries to cut down DiZ, but it is revealed that DiZ was somewhere else, and the one before Roxas was nothing more than a data-based projection. All his anger drains away when he sees Sora slumbering in his pod. With a sad smile, he remarks that his "summer vacation...is over". At this point, the prologue ends.
Hints
Roxas, though he does not truly appear to Sora throughout most of the game, is frequently mentioned. Most of the Organization members call Sora "Roxas", confusing and frustrating him. Also, Roxas manages to maintain a presence within Sora. The first time is when Sora departs from Twilight Town for the first time, saying goodbye to Hayner, Pence, and Olette. To his surprise, a tear rolls down his eye, expressing Roxas' own sadness in separating from his friends. And even they feel a certain connection to Sora, though they had never met before.
During the second visit to Twilight Town, Roxas' presence within Sora is again apparent. As Sora looks through the crystal orb and at the orange sun, he could subconsciously feel Roxas within him.
Finally, during Sora, Donald, and Goofy's brief stay in a realm of nothingness, Riku had left two clues for them, one of which was a picture from the digital Twilight Town, which showed Roxas, Hayner, Pence, and Olette standing in front of the abandoned mansion. Despite Sora having never seen Roxas before, he immediately knows that the name of the boy in picture is Roxas.
Encounter
The hints of Roxas' presence within Sora come to a climax in the World That Never Was. At Memory's Skyscraper, two Samurai Nobodies come and block Sora from Donald and Goofy. Then, Roxas, shrouded in an Organization cloak, confronts Sora. The two are then transported to the Station of Serenity, and the two share an intense battle. When Roxas says that he is someone from the dark, Sora wonders if he is Riku, but Roxas says that he had had defeated a Riku once. He also asks a strange question: "Tell me, why did he choose you?!" At one point, Roxas floats from above, and sees the images of Riku, Kairi, Donald, and Goofy next to Sora, and finally understands. Still, Roxas continues to attack, but Sora in the end defeats him. His face is revealed, and he says "You make a good other".
Sora returns to the World That Never Was, but Donald and Goofy say that they saw no one other than themselves, and Sora had just disappeared, leaving Donald and Goofy to fight some Nobodies.
As Sora make their way up the Organization's stronghold, the Organization makes more and more confusing remarks about Roxas. Eventually, Sora asks why the Organization calls him "Roxas", and Riku reveals that Roxas is his Nobody, giving him the power to use the Keyblade. He also explains that Roxas left the Organization, though Riku realizes that Roxas had left in the first place because he wanted to meet Sora in the first place, and thus didn't have to fight him. Sora sadly expresses that he wants to meet Roxas, but Riku points out that Roxas rests within him.
After Xemnas' seeming defeat, Roxas and Naminé reunite, projecting themselves through Sora and Kairi, respectively. They are happy that they met again, and say that unlike other Nobodies, they got to meet their original selves and become whole. Finally, Roxas and Naminé believe that as long as Sora and Kairi are together, so will they, and accept their place within Sora and Kairi.
Roxas and Naminé are seen one last time, when Sora and Riku return to Destiny Islands. As Sora and Kairi reunite, they smile at each other, while Roxas and Naminé do the same.
Personality
Roxas, unlike other Nobodies, seems to possess emotions, stemming from the fact that he is a special Nobody. He is far more prone to anger than Sora, which DiZ amusingly notes in their encounter. On the other hand, Roxas is notably very melancholy, especially as he comes to realize the truth about himself.
Battle technique
In battle Roxas wields two Keyblades, the Oathkeeper and Oblivion. He controls the element of light and the Samurai Nobodies, possibly due to his acrobatic nature - fans will notice that when he duels with Sora he performs many more stunts than the other Members ever do or, possibly, are capable of (excluding, perhaps, Xemnas who is able to jump to the top of Memory's Skyscraper. However, Roxas and Sora are both able to run up its walls).
It is also worth nothing that Roxas seems to have a far more aggressive style in comparison to Sora: he is constantly on the offensive, and relies little on defense in his battle with Sora.
