The story of Roxas is a... complicated one to say the least. When a person's Heart is consumed by the darkness and converted into a Heartless, the body left behind can sometimes continue to go on with a will of its own. These beings, called Nobodies, lack a Heart and thus the capacity to feel emotions. At least at first. Given enough time, even a Nobody will begin to develop a Heart that serves as a pseudo replacement for the one that was lost.
Roxas is the Nobody of Sora, born at a time when Sora willingly allowed himself to become a Heartless to save his friends. But even among Nobodies, Roxas was still a strange case. Every other Nobody retains either the appearance or memories of the person they once were, sometimes both. Roxas, for
reasons unknown to him, looked and sounded nothing like Sora and nor did he possess any memory at the time of his birth. However he did inherit Sora's ability to wield the Keyblade. And the person who found him saw this as a valuable opportunity.
Roxas was discovered by a fellow Nobody called Xemnas. When he found that Roxas could wield the Keyblade, Xemnas inducted him into Organization XIII as its thirteenth member, and even gave Roxas his name. Within the Organization, Roxas's job was to use the Keyblade to defeat Heartless and release the Hearts they had captured. This was in order for the Organization to achieve its stated goal: to create Kingdom Hearts and use its power to become whole again.
He worked with all of the Organization's members off and on, but the one he latched onto the most was Number VIII, The Flurry of Dancing Flames - named Axel. A few days into his new life, a fourteenth member was inducted into the Organization, a girl named Xion. Trying to help her out the way Axel had initially helped him, Roxas invited her to hang out with the two of them in between missions. The three bonded and became close friends over the course of nearly a year. But during this time, some strange things were happening with Roxas and Xion. During certain periods one or the other would find themselves weakened and unable to summon the Keyblade. And Xion herself later started acting more distant and distracted.
Roxas only learned later what was really happening. As it turned out, Xion was merely a puppet. A Replica capable of very accurately simulating human emotions and behavior. She was created as a backup plan in the event that Roxas ever turned against the Organization, as it very much needed the Keyblade in order to achieve its goal. Even Roxas himself began questioning the missions he was sent on and wondering if their stated goal was even the true aim of their leader. And things took a turn for the tragic when Xion learned the truth about herself, and further learned that she and Roxas would eventually have to return to the person they were both born out of. She would lash out, first against Axel and later against Roxas. But her true aim was simply to goad Roxas into striking her down in order to save himself.
As Xion lay dying in Roxas' arms, he still recalled the times he had spent with her and Axel. Sitting on top of that clock tower and eating those ice creams together. But then, she was gone. And when she was gone, so too was all memory of her. It was like she had been simply erased from ever existing. Roxas could now feel a great deal of pain and heartbreak but no longer could remember why. He decided it was high time he confronted Xemnas for answers, even if it meant he had to take the down the entire Organization to do it. Now possessing the power to wield two Keyblades, Roxas made a move toward his former home.
Before he could confront the Organization, Roxas was stopped by a
cloaked stranger. He had been the one to tell Xion the truth, and now it seemed he was here for Roxas. Roxas refused to budge, and instead attacked the stranger. During their fierce fight, Roxas was able to overpower the boy and nearly won. But then, the boy seemed to transform into another form altogether and suddenly was much stronger. He took Roxas by surprise and knocked him out.
The next thing Roxas knew, he awoke in what he remembered as his home in Twilight Town. He quickly got dressed and ran outside to meet his friends at their usual spot. Unknown to him, what he was living in was little more than a virtual simulation. The memories he appeared to have now were implanted in order to keep him complacent. It seemed that the person he was born from was in the process of being restored, and that meant that Roxas needed to be kept in check for that to happen. After only six days, Roxas did eventually discover the truth. He confronted the
man who had been keeping him in this virtual town, demanding to know the truth and to be set free. The man however just coldly and callously told him that his time was up and that he needed to return to the person he came from so that he may do what was needed to save many people. That was that, Roxas was trapped here with no way out. And no other choice but to accept his fate. He angrily lashed out at first, but realized that this person was the one whose memories he had been having dreams of lately. It was the remaining proof needed to confirm that the man, harsh as he was, was telling the truth.
Looks like my summer vacation... is over. Roxas told himself as he finally returned to the Heart he had been born from. He remained there for some time, silently watching over the person's travels and struggles. Until one day, eventually, he finally had a way to return. It seemed the Organization was using Replicas as a way to allow Hearts to be transferred to other points in time. And as luck would have it, his Other Self's friends had managed to get their hands on one such vessel. That was what gave Roxas the opportunity he needed, and he returned in time to see his former superior about to strike down his two best friends.
"Hands off my friends." he had said, pointing one of his Keyblades at Xemnas in a threatening manner. Alongside Axel, Roxas' Other, and a newly restored Xion among many other new and old friends, Xemnas and the new Organization he had been aligned with was finally defeated for good. The trio was finally able to go back home, to Twilight Town. And while Roxas had believed that his struggles were finally behind him, something else was about to come rippling through and threaten to tear it apart all over again.