we meet again
The story begins with Roxas, a mysterious boy living in Twilight Town with his friends. During the six days, Roxas gradually views the entire span of the first game in his dreams, learning more and more about Sora. He encounters Kairi when thinking it was Namine, and encounters Axel, who has been looking for him. On the sixth day, Roxas finds he is invisible to everyone, and in a hurry, runs to the mansion in the town. He recollects what happened before his days in Twilight Town, encounters Axel one last time, and encounters DiZ, and more importantly, the sleeping Sora. Thus, the game begins.
Sora awakes from his year long slumber and goes in search of Riku, who he had to leave in the world of darkness - and learns more about the Organization who run amock whilst controlling the nobodies, and most commonly, the Dusks. He fights his way through the worlds, learning more and more about both as he goes. Then, he finds Kairi has also been kidnapped by Axel, though, she escaped, but was recaptured by Saix. Sora continues in pursuit till The World That Never Was, along with his majesty, King Mickey. As he climbs through the castle, he enounters Kairi, and is reunited with Riku in the form he took to save Sora. As Ansem gives his life to protect the trio, Mickey, Donald, and Goofy, Riku is returned to his original form. Thus, he and Sora face Xemnas in a battle that reconnects their friendship.
Finally, the two return home, to Kairi, who is waiting there for them. In the last few shots, we see Riku and Sora talking.. then Kairi runs up with a letter from Mickey. What could it hold? We'll have to wait and see..