Answer:
Kingdom Hearts Chain of Memories is the story between the ending of Kingdom Hearts 1 and the beginning of Kingdom Hearts 2. After Sora, Donald and Goofy beats Ansem, they end up on this road next to grass, then they suddenly see Pluto, Mickey's pet dog, with a letter from the king. But as Pluto runs away, they lose him and doesn't know where to go. Then a man in a coat appears, and he talks about a castle. That's where they end up in the story, Castle Oblivion, this is a special castle where the further you go inside, the more memories you lose. Sora first goes in to find Riku, but ends up trying to find Namine, a girl he knew in Destiny Islands and fighting people from Organization XIII. Although he does find Riku, Riku's heart has changed. In the end, Sora finds Namine, but Namine traps Sora in a pod, where he sleeps, and then that's where Kingdom Hearts 2 comes in.