Like Julia could have a High School Cheer theme mixed with electric guitars
Shade's could be one of those horror chases themes from indie horror games
Radomus could have big band jazz
And the circus trio could have a Circus themed battle song
Also, what I usually do is analyze the gym leader's specialty and field. And right before battle, I change the leader theme in the game's files to something more fitting.....am i the only one who does this?