I never really thought of the fight as dark or gritty or anything. I thought it was more of a "shut up, there's no way you're me!" kind of aggression for Sato instead of a "you can't be me...!" kind of denial. Plus, I personally don't find the song that up-beat. It's certainly not close to the P4 Shadow theme in terms of tension/emotion or whatever but I think it fits the bill.