SECRET INVESTIGATOR
This is for the Secret Reports you collect throughout watching the videos and reading through Roxas' diary. After you've done all of these easy things (either through skipping through or genuinely watching) you should have all the Secret Reports. Go to the Roxas' Diary through the menu, then press Triangle in order to start reading the Secret Reports. From there you could just skip through all of them by pressing R1, or you could read them and enjoy the story.