Kingdom Hearts: Birth By Sleep
In Birth By Sleep Sora and Riku are shown as best friends. They are often seen racing, fighting with wooden swords and other competitive stuff on their island. A little before Birth By Sleep Sora’s heart helps heal Ventus’ newly broken one which establishes a connection between them so strong that Vanitas’ face ends up looking like Sora’s.
When Sora is 4 years of age, he encounters Terra and Aqua, 2 keyblade wielders each of whom he meets at a separate time. He never spoke with Terra cause Terra didn’t see Sora’s potential and instead talked to Riku. When he met Aqua she recognized the relationship to be similar to her own with Terra and Ventus and has Sora promise that if Riku felt into Darkness that he would protect him to which Sora promptly agrees. Ventus had also visited the islands but never actually met Sora face to face.
Sora and Riku talk and Riku persuades Sora to see who connected with his heart. Sora then agrees to Ventus who asks if his heart would allow his to slumber there which Sora agrees to.
Sora is a young boy living in the Destiny islands with his best friends Riku and Kairi, as well as other inhabitants. The dream of these young teenagers is to go to leave their homes for adventure in other worlds so they craft a 'boat' to leave their homes. The night before the planned 'trip' day, a storm hits the island and monsters invade. Sora is gifted a keyblade and goes to the beach to make sure the boat is safe. When he arrives there he faces a huge monster (bigger version of the Heartless). After defeating the monster, the big Heartless creates a dark portal in which everything is attracted. Sora ends up in the hole which is pitch black.
Sora wakes up alone in a place called Traverse Town and starts looking for his friends. On his way he meets up with friendly people such as Leon and Aerith that try to help him. He then encounters Donald and Goofy, two soldiers from the King's castle looking for their missing king. Donald is the court wizard for King Mickey, and Goofy is the captain of the royal guard. Together, the trio go on a quest for their missing friends across many worlds from the Disney Universe.
After travelling through many Disney worlds Sora finally finds his friend Kairi. But in order to save her, he must sacrifice his own heart. He does so, but losing his heart turns him into one of the Heartless. Kairi's caring and love for him is able to restore his heart. Afterwords, Sora, Goofy and Donald face off against the evil Ansem. They defeat him, but in order to close the gates of Kingdom Hearts, King Mickey and Riku must close it from the other side. Kairi is sent back to the Destiny Islands, but Sora, Donald and Goofy set off to go find Riku and the King.
Sora's story was continued in the Game Boy Advance game: Chain of Memories. While they are looking for the King and Riku, they stumble across a large castle, Castle Oblivion. Inside, Sora has to use cards in order to advance further through the castle. The consequence of that is that they will lose more and more memories the higher up they go. As they progress they begin to remember the ones that they are looking for but also begin to lose thought about the ones that they have already known. Sora has repetitive encounters with Dark Riku in the castle as they progress, ultimately meeting up with the one who has control over Sora's memories, her name is Naminé (Nah-men-ney).
In order for Sora to regain the memories he has lost while progressing through the tower, Sora, Donald, and Goofy must all enter pods in order for Naminé to rewrite the memories that they have all lost while searching for her. While Sora was losing memories in Castle Oblivion, Roxas (Sora's famous duel-wielding Nobody) was being created and finally was created at the end of Chain of Memories. It is said that Sora, Donald, and Goofy have been in the pods for one entire year, before the events in Kingdom Hearts 2 transpired.
Sora's story was continued further in Kingdom Hearts II. Sora awakens in his clothes from the first game which are very small now and then meets Yen Sid, King Mickey's Master. Yen Sid explains everything that has happened over the year Sora has slept and the things Sora, Donald, and Goofy will be expecting. The first world they go to is Hollow Bastion where the group meets up with all their old friends like Leon, Cloud, Yuffie, Aerith, Cid, and Merlin. In Hollow Bastion they finally meet the Organization XIII.
The group leaves on the gummi ship to The Land of Dragons where they meet Mulan and see Mushi again. The group helps Mulan save China from Shan Yu. Next the gang meets up with Beast at his castle where he is having some problems. They help Beast get rid of Xaldin. Then, they go to see Hercules and help him and Auron from Hades. Next they go to Disney Castle which is being over run by Heartless so the group has to go through this door which sends them back in time so they can get rid of the Heartless. Next, they go to Port Royal and meet Jack Sparrow and help him out. Then they got to help out Aladdin and then they go to help Jack Skellington. Next, the group is all turned in to an animal(sora a lion, goofy a turtle, and donald a bird( he does become a duck, a different bird) in the Pride Lands. The group then revisits all of the worlds that helped out origanally because something new has happened. The last world they vist is The World That Never Was.
There they meet up with Riku and Kairi. So, the group then defeats all of the remaining members of the Organization XIII. In the end you see Sora, Riku, and Kairi get a letter from King Mickey, ending the game. Sora is going on a quest to help save his friends after reading the note that the king sent...it is heavily hinted that Aqua, Ventus, and Terra are related to this…