It's exactly what it sounds like. It's Sonic, but it's Zack Fair from Final Fantasy VII.
I originally uploaded this the day before the contest and expo were taking entries, and it had 2 options, as well as the music being it's own file, but for convinience I included the music here (only in boss fights). Option 1 was the 1st Class, Black Turtle Neck from Crisis Core, but it's visually boring since it's 80% Black and Grey, so I made Option 2, which was the Purple Turtle Neck, from when he was 2nd Class, and in the original where it was also purple. This mod includes the purple one.
Square Enix - Creating Final Fantasy
Takeharu Ishimoto, and Kazuhiko Toyama - Composing the soundtrack to Crisis Core: FFVII
Nick (he's not a guy I know or anything, that's just the name of the YouTube Channel) - Creating the song used for Final Hazard
Nobuo Uematsu - Composing the soundtrack to Final Fantasy VII