This is so fun — I can totally see myself using it for some Scott Pilgrim gaming. It's just the right amount of heightened.
You've packed a lot of structure and support into a small package and the tone is great. I'd love to see it with a layout and art that amplified what you're already doing in the text.
My one rules concern: It seems like the Band Battles rules strongly encourage characters to specialize in one of the roles and just keep spamming that one move. Is that the idea? (To be fair, it's pretty accurate to my real-life band experiences!) If not, maybe there's a way to encourage characters to branch out? Maybe they can't use the same move twice in a row? Or maybe they have to use each one at least once in a battle (and the fourth is their choice)?
Anyway, this is minor stuff. Very cool!