Welcome back to the main plot.
I know we've spoken about the big twist well before it came into play here, but I still think it's a really great moment. The big reveal that Sora was *never* supposed to be the hero. His status as a keyblade bearer, and his numerous successes, can be attributed to a happy accident.
It's the part of the story where the hero hits rock bottom, and everything is stolen from him. Fortunately, this sets up one of my favorite scenes in the game. After reflecting on his journey, Sora realizes that he can keep going without the keyblade. It's a powerful scene, especially in the context of this story.
Sam makes a great point in that this especially highlights the dichotomy between Sora and Riku and how they see the world. Unlike Riku, Sora went out, saw the world, and met all kinds of people, so he learned the value of friendship. Despite leaving his island home, Riku remained isolated, and ultimately gave into the darkness. It's not original, but it's a plot that works.