First of all this story has major spoilers for both kingdom hearts coded and kingdom hearts birth by sleep. It has what the letter Mickey sent at the and of kingdom hearts 2. Now first of all I don't own the characters but I own any made up characters and the plot from the next chapter is mine too.
Chapter One
The Letter That Started It All
Sora was running towards Riku who was sitting on the papou tree.
"Nothings changed, huh" Riku said
"Nope nothing will" Sora replied
"What a small world" Riku started
"But part of one that's much bigger" Sora finished
"Yeah" Riku replied
"Hey Riku what do you think it was the door to the light" Sora asked
Riku laughed a bit and jumped down and pointed at Sora's heart
"This" Riku answered
Sora touched his chest
"This" Sora confused
"Yeah its always closer than you think" Riku said
Sora smiled
"Sora, Riku" Kairi shouted
Kairi was carrying a bottle with a letter inside
"Hey what's up" Sora asked
"Look" Kairi answered
There was the kings seal
"From the king" Sora said shocked
He quickly opened it with Kairi and Riku at his side, the letter said this
I wanted to tell you immediately. There are memories asleep inside you. Those memory fragments connect to the future. Sora, Riku, Kairi, the truth surrounding the Keyblade, passes through numerous connections, which are inside your hearts. Sora, it all leads to you, and everyone is waiting for you. The only one who can heal their sadness is you. Its possible that the travels up until now, compared to the next trip, may have been easy. Everything thought to be accidental was really connected, and the door to a new departure already seems to be opening. -Mickey