If you look at your Battle Rally courses you will see tiny little stars above the number of the course you are selecting. The game wants you to get a high score with each character on each course. Maybe there is something extra to unlock if you high score them all with the three. I've been a Ren loyalist and I just notice this.
And I want to say thank you for your guides, your video “All 120 Bailu Chan” helped me a lot.