ROXAS---According to the Secret Ansem Reports, Roxas was born when Sora stabbed himself with the Keyblade of People's Hearts forged from the hearts of six of the seven Princesses of Heart in order to free Kairi's heart at the cost of his own. However, Sora spent little time as a Heartless, as Kairi's light had fetched Sora's heart from the darkness, restoring him to his former self shortly after he first became a Heartless.
Thus, Sora and Roxas co-existed, but Roxas was missing his memories, the memories of Sora, and the two were incomplete without one another. Still, Roxas's status as Sora's Nobody granted him the ability to use the Keyblade. This, as well as his capacity to experience actual human emotions, something that Nobodies are normally incapable of, makes Roxas a very unusual Nobody. However, as he wields a Keyblade, which serves as a homing beacon for the Heartless, he is constantly under risk of being attacked by them when not under the protection of other Organization members.
Roxas and Xemnas talked along the bank of the Dark Realm, the Dark Margin. This is where Xemnas said that he had been to see him (referring to Sora). This is referring to when he was a secret boss in Kingdom Hearts Final Mix.
Roxas also appears to have a psychic link with Sora, as he begins to absorb Sora's memories as Naminé restores them and falls into a coma right when Sora was put to sleep.
Sora visits Twilight Town after Vexen gives him the world card. Sora doesn't recognize the world, but Donald and Goofy point out that he must, as it was created from his memories. Vexen tells Sora that it was made from the memories found on the other side of his heart. This references to Roxas as Vexen met Roxas before leaving for Castle Oblivion.
After finishing Riku's Story, there is a picture of Roxas that is shown after the credits. This was altered into a silent cutscene in Kingdom Hearts Re:Chain of Memories with Roxas seen with Hayner, Pence, and Olette. During the end credits, Axel is seen to converse with him, but Roxas completely oblivious to his presence.
Roxas was "born" in Twilight Town and soon discovered by Xemnas, who gave him his name. Having nowhere else to go, Roxas joins the Organization in hopes of finding the answers he needs. On Roxas's 6th day, he is summoned by Xemnas to the Dark Margin in the Realm of Darkness. Having met Sora during his visit to Hollow Bastion, Xemnas mentioned the boy's resemblance to Roxas. Roxas asks just who he is, but Xemnas only explains just what he is. When Roxas repeats the question, Xemnas states that his name is of no importance and asks Roxas if he remembers his own true name. Roxas attempts to answer, but then realizes that he doesn't know as Xemnas reveals the youth's identity as Sora's Nobody.
Two days after, Xemnas places Roxas under Axel's watch, and the two soon become best friends. When he visits Twilight Town, sometimes he catches sight of three regular kids: Hayner, Pence, and Olette, and wishes to befriend them. The following days, Roxas is trained by Marluxia, Vexen, Zexion, Larxene, and Lexaeus to hone his abilities while understanding the covert missions he would carry for the Organization. When Axel is sent to Castle Oblivion to interfere in Marluxia's plans to enslave Sora and overthrow Xemnas, Roxas is placed in charge of Xion, the newest member of the Organization and a girl about the same physical age as him.
Though emotionally distant at first, Xion soon opens up to Roxas, revealing to him that she can wield a Keyblade, and the two become close friends. Afterward, due to Sora being placed in suspended animation by Naminé, Roxas falls into a coma for several weeks. After awakening, Roxas attempts to spend time with Axel and Xion, but he begins to react to the process of Sora's memory restoration, and begins to question why he wields the Keyblade and doubt the Organization's motives. The memories manifest more during Roxas's missions.
As he spends more time with the Organization, Roxas grows increasingly impatient towards his unanswered questions. Meanwhile, he still works actively to assist the Organization in their plan for Kingdom Hearts, using the Keyblade to release the hearts within the Heartless. However, Xion, seeking answers to her own questions, departs the Organization to find herself. Roxas soon follows her example and defects from the Organization himself. On his way, he is intercepted by Axel, who attempts to persuade him to stay, warning him that the Organization would destroy him due to his betrayal. However, Roxas remains indifferent, saying "No one would miss me", and continues on his way. Axel yells at him, "It's not true!" and in a quieter tone, he admits he would miss Roxas.
At some point, Roxas, while searching Twilight Town, encounters Xion, who has discovered the truth behind her own birth (that she is not a Nobody, but an imperfect replica of Roxas created from Sora's leaked memories by Xemnas in the event that Sora turned out to be useless to his plans for Kingdom Hearts) and is reprogrammed by Xemnas. Roxas is shocked to discover that Xion has taken on the appearance of his past self, and even more so when he discovers that Xion desires to become the 'real' Sora, and wants to absorb Roxas stating it was the reason why she was created.
This is shown to be nothing but a ruse, in connection to her thoughts by her Secret Reports. She is aware that they cannot coexist, that Roxas was in danger if so, and decided to willingly disappear, and not let Xemnas succeed: a fact that she states when she later dies.
Knowing that Roxas would not be able to kill her, and Axel had admitted that he could not either in his own Secret Report, she forces Roxas to fight her instead. Xion then transforms into a giant armored monster at the ready. After a long and grueling battle, Roxas defeats Xion, who regains her original appearance. Roxas, however, loses all of his memories of Xion after the battle. In her final moments, she informs Roxas of the true colors of the Organization, tells him that she is glad they were friends and pleads with him not to let Xemnas accomplish Kingdom Hearts before dying peacefully in his arms. At this moment, Roxas remembers Xion, but he is too late. Saddened, Roxas holds Xion's essence and degenerating crystallized body until she is completely gone, leaving behind a seashell on the ground, as he spills tears.
This marks the start of where he gains his signature ability to dual-wield, as he awakens Ventus's Keyblade after Xion's demise. The first time he uses them, they appear as two Kingdom Keys, his and Ventus's, which quickly transform into the Oathkeeper & Oblivion.
Xion's absorption into Roxas, along with the knowledge of Xemnas's true plans, only further strengthens Roxas's determination to find Sora and the answers that he seeks. Before that, however, Roxas returns to The World That Never Was, planning to "set Kingdom Hearts free", in compliance to Xion's last words. He also desires to save Xion from within him, hoping that freeing Kingdom Hearts would bring her back and then they could go back to Axel. Upon his arrival, Roxas is attacked at Memory's Skyscraper by countless Neoshadow Heartless, which surround him.
Roxas draws out his Keyblades, ready to defend himself. However, even after slaying many Heartless, he realizes there are too many to fight alone.
Luckily, Riku suddenly appears at the scene on top of the Skyscraper, and Roxas tosses him his Oblivion Keyblade as he runs up, and they both defeat the Neoshadows once on the ground. However, both immediately turn on each other when done. Roxas beats Riku at first, but Riku taunts him by calling him "Sora" and saying that he should be "stronger than this", causing Roxas to reflexively answer with, "Get real. Look at which one of us is winning", something that only Sora would say.
Riku willingly unleashes his inner darkness and takes on the physical appearance of Ansem, Seeker of Darkness. Riku-Ansem disappears and reappears in front of Roxas, surprising him, before the Guardian grabs him and squeezes him hard enough to make him lose consciousness. DiZ then appears and opens up a portal to the old mansion in Twilight Town, where DiZ resides.
DiZ aims to join Sora and Roxas together in order to help Sora wake up faster after regaining his memories. However, he knows the Organization is hunting fervently for their missing member, so DiZ places him in a virtual Twilight Town. There, Roxas would be kept safely away from the Organization while he lived as a normal boy, unaware of his past. Even though Roxas begins to forget about Xion, she tells him that she'll always remember him and Axel. It showed that when Roxas began to forget, cutscenes including him, Axel, and Xion were changed by Xion being erased.
Somehow, DiZ was able to alter Roxas's mind to cause him to believe that he lives a normal life in the digital Twilight Town. He has become best friends with three kids: Hayner, Pence, and Olette and even writes a diary of his time in town. It is this time in the digital Twilight Town that serves as the prologue to Kingdom Hearts II, similar to Destiny Islands in Kingdom Hearts. Roxas has lost all memory of his life with the Organization.
As Naminé nears the completion of the task of restoring Sora's memories, Roxas soon begins seeing brief fleeting memories of Sora through a number of his dreams. In addition, mysterious events start to occur around town. Strange white creatures, the Nobodies, begin invading the town, stealing photographs and attacking Roxas. These Nobodies had been sent along with Axel by the Organization, who had finally located their former member, in an attempt to capture him. However, in times of dire need, the Keyblade (a single Kingdom Key this time) inexplicably comes to aid Roxas, and disappears once the threat is gone.
Along with the Nobodies, Roxas comes into contact with Naminé several times, who seems to know things about Roxas that he himself doesn't and once saves him from the outburst of darkness resulting from the defeat of the Twilight Thorn on day three inside Roxas's Dive to the Heart.
Furthermore, as observed by DiZ, Naminé's contact with Roxas connects his heart with Kairi's, who Roxas remembered as a friend of Sora. He also meets a mysterious man in a Black Cloak, later revealed to be Riku, who at one point asks a cryptic question: "Can you feel Sora?" Roxas later meets another mysterious figure masked in red bandages, DiZ, who was responsible for his imprisonment.
Though the intentions of these characters are enigmatic to Roxas, Axel soon appears with a more straightforward goal. Axel needs to bring Roxas back with him under the orders of Xaldin and Xemnas. However, Roxas remembers nothing of Axel, whose claims of his relation with Roxas only confuses Roxas. Axel is soon forced to attack the young boy to accomplish his goal. He battles Roxas in the midst of the Struggle tournament, but only DiZ's timely interruption spares Roxas from defeat.
After the Struggle Tournament, Roxas falls off the Station Tower and somehow mentally attempts to contact Naminé, only to end up reaching Kairi, Naminé's true counterpart, instead. He recognizes her name from his dreams of Sora, and when Kairi inquires Sora's name, Sora himself, despite being asleep at that time, talks to Kairi through Roxas and gives her a hint of his name (Starts with an "S"...).
In addition to these mysterious people, Roxas also begins to see strange anomalies due to the nature of Digital Twilight Town. Time often freezes, and only he and select people seem to be unaffected. He also sees strange "glitches" around town that he could not explain. For some time, Roxas continues to be befuddled by all these events.
That all changes when summer vacation comes to a close, and the truth is revealed: Naminé informs Roxas that he is a Nobody, and that he is supposed to meet with Sora, the boy in red from his dreams, in order to complete him. Along with that, Roxas discovers that he is living in a digital Twilight Town, and that his friends aren't real, just data. He encounters Axel once again, who had been ordered to eliminate Roxas if he refused to return. DiZ, however, manages to freeze Axel in his tracks, along with the rest of the world, thus saving Roxas. DiZ then tells him to go to the abandoned mansion. He does so, and there he encounters Naminé.
She reveals to him information on Organization XIII and states that reuniting with Sora would not cause him to disappear, but make him whole. However, she is interrupted by DiZ, but before she is taken away, she promises him that they would meet again, even if they won't recognize each other. Desiring to see Sora, Roxas makes his way through the mansion and begins to recall his former life. In doing so he realizes that he had been captured and placed into the digital world by DiZ and the mysterious cloaked man. Roxas then destroys DiZ's computer in anger, even though it was just a digital copy.
Roxas then meets with Axel one last time, but despite the fact that Roxas has regained his memories, Axel states that it is too late. The two battle once more, but this time Roxas is able to call on all of his dormant abilities, including summoning his two weapons: Oathkeeper and Oblivion, and soundly defeats his old friend, though with great regret. Roxas hopes that they will meet again, though Axel chuckles and responds that only Roxas has a next life. Axel then retreats into the darkness, failing in his mission to capture or kill Roxas. Roxas then enters the pod room where Sora is kept, but not before seeing Donald Duck and Goofy slumbering in their own pods. DiZ is there to greet him, revealing his intentions and fueling Roxas's rage with cutting remarks about Roxas's purpose and nature.
In a blind rage, Roxas tries to cut down DiZ, but sees that this DiZ is only a hologram; even after this, Roxas continues to attack DiZ. He vanishes, and the pod in the center of the room opens. All his anger drains away when he sees Sora slumbering in the pod. Sadly smiling, he says to Sora, "You're lucky... Looks like my summer vacation is... over". With those words, Roxas respectfully accepts his fate and rejoins with his original self.
Right after the prologue ends, Sora hears Roxas call out to him, and wonders who it is before hearing Donald and Goofy do the same and waking up.
Though he does not actually appear to Sora throughout most of the game, Roxas is frequently mentioned. Most of the Organization members act as if Sora is Roxas and refer to him as such, which both frustrates and confuses Sora. Roxas himself manages to maintain a presence within Sora despite "resting". The first time this is hinted at 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 cheek, expressing Roxas's own sadness in separating from his own friends, and feels strangely sad to be leaving Twilight Town. Sora instinctively knows how to ride a skateboard, (a skill that was not touched upon in the first game) and is shown to be very skilled in doing so; presumably, this is an ability passed down from Roxas.
During the second visit to Twilight Town, Roxas's presence within Sora is again apparent. As Sora looks through the crystal orb and at the orange sun, he subconsciously feels Roxas truly within him, and briefly takes on Roxas's appearance as he does so (at least to the player). Then, during Sora, Donald, and Goofy's brief stay in a Realm of Darkness after the Battle of the 1000 Heartless, Riku leaves two clues for them, one of which is a picture from the digital Twilight Town which shows Roxas, Hayner, Pence, and Olette standing in front of the abandoned mansion at Twilight Town.
Despite Sora having never seen or met Roxas before, he immediately knows his name. When Sora, Donald, Goofy, and Mickey enter the digital Twilight Town, Sora calls it "Roxas's Twilight Town", and we are then shown a flashback of Roxas destroying the computers. It is also made apparent that Axel is determined to transform Sora into a Heartless; if Sora became a Heartless, then Roxas would be reborn.
Finally, a dying Axel reveals his intent to Sora and his relation to Roxas before fading into nothingness from using all his energy. His death, as Xemnas said, was strong enough to finally, truly awaken Roxas at last. Only after the death of Saïx does Sora find out why the Organization thought that he and Roxas are one and the same.
The hints of Roxas's presence within Sora come to a climax in the World That Never Was. At Memory's Skyscraper, two Samurai Nobodies arrive and block Sora from Donald and Goofy. Then, Roxas, shrouded in a Black Coat, confronts Sora, summoning his Keyblades (much to Sora's surprise). The two are transported to the Station of Serenity, and they share an intense battle, which was originally depicted in a short cutscene, but became an actual boss battle in Kingdom Hearts II Final Mix.
During their fight, Roxas says that he is someone from the dark, and Sora wonders if he is Riku. His guess is incorrect, and Roxas says that he had defeated a Riku once. He also asks a strange question: "Tell me... Tell me why he picked you!" and attacks Sora in a rage.
At one point, Roxas floats from above, and sees the images of Riku, Kairi, Donald, and Goofy next to Sora, and finally understands that Sora has the Keyblade because of the bond with his friends. Still, Roxas continues to attack, and is able to knock the Keyblade out of Sora's hands. Sora, however, recovers the Keyblade and swiftly cuts a surprised Roxas down. Roxas, wounded, drops his weapons and his hood, revealing his face, and tells Sora, "You make a good other", disappearing with a satisfied look.
It is revealed that the encounter was actually a mental struggle between Roxas and Sora when Sora returns to the World That Never Was. He asks his companions about the mysterious Keyblade-wielding Nobody, but Donald and Goofy say that they saw no one other than themselves, and that Sora had just disappeared, leaving them to fight some Nobodies. Sora is confused, but continues on.
As Sora makes his way up the Organization's stronghold, the Organization members, before being cut down one by one, make more and more confusing remarks about Roxas. Upon Saïx's loss, Sora questions why the Organization calls him "Roxas", and Riku reveals that Roxas is his Nobody, which gave Roxas the power to use the Keyblade. Sora is taken aback by this at first, but then remembers his brief transformation into a Heartless while attempting to rescue Kairi. Riku also explains that Roxas left the Organization, and Riku tried to bring him to DiZ, but was defeated. Riku then took on the form of Xehanort's Heartless and used the darkness as a weapon.
He managed to bring Roxas back so that he may join with Sora in order to awaken him from his sleep. However, Riku realized that Roxas had left in the first place because he really wanted to meet Sora, and thus Riku didn't have to fight him. Sora sadly expresses that he wants to meet Roxas as well, not knowing that he had already met him during their battle at Memory's Skyscraper. Riku then points out that Roxas rests within him. On their way to fight Xemnas, DiZ (now revealed to be the real Ansem, Ansem the Wise) apologizes to Roxas for his mistreatment of him, though he didn't know whether or not he could hear him.
After Xemnas's seeming defeat and the demise of most of the Organization members, Roxas and Naminé reunite, with Roxas projecting himself through Sora after Naminé joins with Kairi. 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, they will be also, and accept their place within Sora and Kairi after being promised by their counterparts that they would always be together. With that, both Nobodies merge back with their original selves. Even though Roxas is gone at this point, he can be considered present when Sora and Riku go into the final boss battles against Xemnas, since Roxas and Sora are technically in the same body when Xemnas is killed.
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. With the death of Xemnas, Roxas could be considered the only surviving member of Organization XIII, if only an ex-member.