Perfected World Is Mine on Extreme.
This song has a lot of fast notes streams that change buttons in the middle. Luckily the beats are easy to follow, so I just have to focus on what button to press. It took me several tries, and on my last try I used 3 help item chances.
So I have perfected all versions of World Is Mine on both Project Diva and Project Diva 2nd. It’s the first song in Project Diva and I have fond memories of it. I wonder if the game developers will also include this song in Project Diva 3rd.. :p