"That was the last straw! I had it with Twilight Sparkle--excuse me--Princess Twilight Sparkle, trying to come back into my life! I had it with her stupid attempts to try and rekindle whatever friendship that I thought we had. I had it with her!"
When Sora ends up on a completely different world, he discovers that he has no memory of who he is except for his name. If he doesn't unravel the mystery behind his missing memories, this world and many others will be in danger.