I was inspired by Darkheart3 to fantasize about if I were in Kingdom Hearts...
I will release it in parts. I will write more parts when I have time.
Part 1: The Quest
Luke was a young boy from Traverse Town. He was training under Leon and Yuffie to take on the Heartless. One day, Leon told Luke of his encounter with Sora. Fascinated, Luke asked Leon to tell him more about the Keyblade. Luke decided to go on a quest to find the Keyblade Master.
Part 2: Hollow Bastion
Luke followed Sora's trail to Hollow Bastion. He made his way to the Grand Hall. There, Maleficent imprisoned him inside the castle wall. Luke witnessed Darkheart being transformed into the Behemoth, as well as the battle between Riku and Sora. When Sora turned the Keyblade on himself to save Kairi, the power to wield the Keyblade entered Luke. Luke held the Kingdom Key until Sora regained his body and the Keyblade returned to him. Luke sat there for what seemed like an eternity, until Leon, Yuffie, and Aerith found and released him. Then they gave him a lift back to Traverse Town.
Part 3: End of the World
Luke needed a gummi ship, but didn't have enough munny to build one. To earn some cash, he helped the moogles in creating a new ability, the Synch Blade ability. With the help of Cid, Luke built a ship, and flew to End of the World. He then fought Ansem and wanted to finish him, but like Donald and Goofy, couldn't enter the impact crater. Then he was trapped in the World of Chaos, and was released when the main core was destroyed. He hurried back to his gummi ship for a package of 10 Megalixers to give to Sora, but was caught in End of the World's cataclysm.
Part 4: The Void
Somehow Luke's heart found its way to the other side of the door, where King Mickey and Riku had ended up. His heart entered the body of Demy, but his past memories were lost. He remembered only the words "Synch Blade" and that he was supposed to find Sora. He took the name "Synchblade" as his past name was forgotten. In the void, he met Darkheart, who gave him the Lost Memory keychain. Now that Synchblade had a decent weapon again, he wandered aimlessly through the void until he came to The Castle That Never Was. There he met Organization XIII and became good friends with Roxas.He also learned that Demyx was his nobody. Through this, Synchblade concluded that his name must be Demy.
Part 5: Sora At Last
Once again, Demy set off to find Sora, following his trail through every world. Demy finally found Sora in The World That Never Was. Demy was overjoyed to have finally found the key bearer (or bearers, as he learned from Riku.) He came with them to Xemnas. There he learned of Xemnas' true intentions. Xemnas trapped Demy's heart and used its strength against Sora. Demy's heart was released when Xemnas was destroyed.
Part 6: Data World and Bug Blox
Demy returned to the Destiny Islands with Sora and Riku, where he learned that this was where his past body and memories lie. Demy was summoned to Disney Castle to help with some computer issues, but he still longed to unlock the memories trapped inside Luke's body. He arrived at Disney Castle where Jiminy explained their dilemma: the computer needed a special Keyblade chip right away. Otherwise, Data Sora would have no weapon. Demy installed the chip, but this aroused the anger of Data Maleficent. Maleficent sucked him into the Data World where he was trapped. Having extensive knowledge of such things, Demy rewired the CPU to create an exit to the outside world. This also created the Bug Blox, some of which grew to become a nuisance for Data Sora.
Part 7: Lost Friends
Demy took his Mark of Mastery exam about a week after Sora, Riku, and Darkheart took theirs. He had witnessed one of these before when he was very young. He passed, and was sent to assist in the search for Terra and Ventus. It seemed that Darkheart had already accomplished this, so Demy returned to the Mysterious Tower. He learned from Yen Sid that Darkheart's heart had to be released. Demy insisted (as most desperate people would, even if they know it's not true) that there must be another way. He rushed upstairs and burst into the room just in time to see Darkheart stab himself with the X-Blade, and disappear into darkness.
Part 8: Restored Memories
Meanwhile, in a galaxy far, far away, Luke had awakened *cue Sora's character theme*. When Darkheart released himself, Luke was restored. Of course, he still had no heart, so he decided to call himself Kexul. He learned of what had happened to his heart, so he hurried to the Mysterious Tower. Kexul and Demy stared at each other in silence. Then, they conversed with Yen Sid on what must be done. Both thought it rather strange to have your other half in the same room. Yen Sid finally decided that the memories must be fused together. This meant that Demy's heart must find a new body for the fusion to take place. How this would happen was another question.
Part 9: A New Beginning
Yen Sid explained that the X-Blade would be the safest way to perform the transformation. However, as Darkheart was gone, he suggested that Riku summon the Keyblade of People's Hearts. This was the only other way possible. However, there was a risk that Kexul and Demy's inner darkness would be unleashed. They decided it was worth the risk. The only other problem was finding a body. The three sat for hours, thinking. Finally Demy suggested that they use the body of Demyx. After all, he wasn't using it since Sora defeated him. So it was decided. Riku stabbed them both, and with a great deal of concentration, directed the heart and memories into Demyx. There was silent anticipation, and then, Demyx sat up. It had worked! Demyx did remark that some darkness had been released, and soon discovered he could enter a Dark State, much like Riku's Dark Mode. Once again, he renamed himself. This time he returned to the name Synchblade (Synchblade Mark II to be exact.) Synchblade was ready for whatever the following days would throw at him.