SORA----Sora and Riku are shown as best friends and rivals as they grew up. They are often seen around the islands battling with wooden swords, racing, and doing anything else that is competitive.
Some time prior to Kingdom Hearts Birth by Sleep, Sora's newly born heart encounters the injured heart of Ventus and mends it, offering to help him restore his broken heart until help is not needed. This allows them to form a connection with one another, and causes Vanitas's face to resemble Sora's.
By the time Sora is four years old, he encounters Terra and Aqua, two Keyblade wielders of the generation before him, on separate occasions. He never spoke with Terra, but they have seen each other on Destiny Islands. Terra shows no interest in Sora because he is unable to sense his potential, and is instead attracted to Riku. Aqua recognizes their friendship as hers to Terra and Ventus and tells Sora to protect Riku if he were to fall into the hands of darkness, which he agrees. Ventus had visited the islands multiple times, but had never met Sora face to face.
Near the ending of Kingdom Hearts Birth by Sleep, Sora and Riku rest on a beach. When they prepare to go home, Sora suddenly feels sad and sheds a single tear. Riku tells him that perhaps someone from another world connected to him is sad somewhere and tells him to try to reach him. Sora closes his eyes and reaches out, which results in him being sent to the Awakening and encountering Ventus's lost heart. It had lost its path and must return to slumber, though it is reluctant to do so and asks if it could become a part of Sora's heart. Sora accepts the request saying that as long as he can make it happy by doing so, he is willing to.
One year after the events of Kingdom Hearts Birth by Sleep, a mysterious little girl named Kairi came to their islands from a different place. She was adopted by the mayor, and Sora and Riku quickly became friends with her. Another day, Sora and Riku found a small, hidden cave on their islands. They search the "Secret Place" while discussing Kairi and the meteor shower that had recently fallen. They find a door with no handle at the back of the cave and, because they couldn't open it, they leave, but not before Riku sees the world's Keyhole.
During their childhood, Sora, Riku, and Kairi often wonder about what lay beyond their small world. By the time they reach adolescence, they decide to build a raft, in the hopes of sailing to other worlds. The day when they start construction, Sora dozes off on the shore of the beach, and has an odd dream where he travels through an odd, dark realm and battles a massive dark creature. Sora is awakened by Kairi, and he goes to help get the provisions for the raft. However, the night before they set sail, a storm ravages the island along with a strange, dark force. Riku succumbs to the force, claiming he is not afraid of the darkness it so clearly embodied, while Sora tries and fails to save his friend from the darkness.
However, it is during the tempest that Sora first unlocks his potential as a Keyblade wielder, summoning the power of the Kingdom Key to battle the Heartless that now infested his home. He makes his way to the Secret Place where he finds Kairi, who disappears when their bodies meet, forcing Sora to battle the same dark creature from his dream. Sora defeats the monster, but he is swept off the island and thrown into a Corridor of Darkness, which lands him in a world called Traverse Town.
In Traverse Town, Sora meets Donald Duck and Goofy, the respective Royal Court Magician and Captain of the Royal Guard of Disney Castle. Under orders from The King, the pair are searching for two things: a mysterious 'key' and a man called Leon. As the King has disappeared in his own quest, Donald and Goofy accompany Sora and they start searching for their respective friends. In addition to that, Sora finds that his Keyblade might perhaps be the mysterious key the King had asked them to find. 
Sora discovers that Riku is also searching for Kairi, though neither of them can find her. Maleficent sees her chance and tells Riku that Sora had replaced him and Kairi for Donald, Goofy, and the Keyblade. With this false knowledge, he sets out to find Kairi on his own as Sora travels to a number of worlds to stop the Heartless. From there, Sora locks the Keyholes out from the reach of the Darkness to protect the worlds' hearts.
His quest allows him to make countless new friends while the power of his heart increases, which also improves his Keyblade's power.
Upon reaching Hollow Bastion, Riku confronts Sora and reveals to him that Riku himself was the true Keyblade master, explaining that Sora "was just the delivery boy". Riku then claims the Keyblade for his own. Despite their guilt at doing so, Donald and Goofy are forced to abandon Sora because of the King's orders: to stay with whoever has the Keyblade. When Beast pulls himself up to continue to the castle, Sora tells him to be careful due to his injuries. However, Beast shrugs off Sora's worries, saying that he would not leave before he completed what he'd come there for; to find Belle. When asked what he came for, Sora realizes that he needs to show the same attitude as the Beast, and continues with him into the entrance hall of the castle.
There Sora meets Riku, Goofy, and Donald once more. Feeling guilty, Donald and Goofy return to Sora's side. Riku then asks Sora, "How do you intend to fight without a weapon?" to which Sora answers, "I don't need the Keyblade. I've got a better weapon. My heart!". Riku taunts Sora, calling his heart pathetic and weak. Sora proceeds to tell him that his friends strengthen his heart. At this, the Keyblade realizes that Riku has turned to darkness, and Sora's heart is far stronger than Riku's, so it returns to Sora. Enraged, Riku fights Sora and loses. Furious at his weakness, he makes the mistake of listening to a mysterious man. Opening his heart fully to darkness, he allows himself to be possessed by this man.
After this, the party encounter Maleficent and defeat her. Using a Keyblade born of six of the Princesses of Hearts' hearts, Riku unlocks the darkness in her heart before stepping away through a Corridor of Darkness. She transforms into a black, fire-breathing dragon from the proliferation of darkness in her heart, but is again defeated and the Heartless swallow her heart. Further into the depths of Hollow Bastion, Sora encounters Riku once more, and he calls himself "Ansem, Seeker of Darkness", who intends to find Kingdom Hearts itself. Although it is difficult fighting his best friend, Sora emerges victorious in the struggle.
Kairi is revealed to be one of the Seven Princesses of Heart who possess the power to open the Final Keyhole that leads to Kingdom Hearts, but because her heart laid within Sora, it cannot open, as explained by "Ansem". In order to return her heart and wake her up, Sora uses the Keyblade of People's Hearts to remove both their hearts, sacrificing his humanity and becoming a Heartless, unknowingly creating Roxas and Naminé, the Nobodies of Sora and Kairi respectively. When he manages to reunite with Kairi after a brief stint as a Heartless, Kairi uses her light to restore his human form.
After regrouping in Traverse Town, Sora decides to return to Hollow Bastion to seal the Final Keyhole while he tries to reclaim Riku from the clutches of "Ansem". Kairi gives Sora her lucky charm (Oathkeeper's keychain) since he insists that she should stay behind, even joking that she would be in his way.
Sora, Donald, and Goofy set sail to Hollow Bastion and seal the Final Keyhole after a battle with a powerful Heartless. The six Princesses of Heart then inform him of a new darkness approaching, and the trio travel to End of the World, the "Heartless world" of all the worlds that fell into darkness, where they confront and defeat "Ansem" once and for all. "Ansem", defeated, calls forth to Kingdom Hearts to fill him with the power of darkness, but Sora proclaims that Kingdom Hearts is not darkness, but light, and "Ansem" is destroyed by the said light.
However, Heartless begin to swarm inside of the door and Sora, Donald, and Goofy rush forward to close it. As they attempt to close the Door to Darkness, Riku and King Mickey appear on the other side of the door and together, King Mickey and Sora seal it from both sides with Sora's Keyblade from the Realm of light and Mickey's Keyblade from the Realm of Darkness. However, Mickey and Riku become trapped behind the door as it closed shut. Riku's last words to Sora before it closed are "Take care of her", referring to Kairi.
As the worlds begin to restore themselves, Sora sees Kairi on a platform of sand that is drifting away. Kairi and Sora are separated with Kairi going back to Destiny Islands. Sora promises to return to her as soon as he finds Riku and King Mickey. 