Cars All cars
At the “Press Start” screen, press Up(2), Down(2), Left, Right, Left, Right, B, A, B to unlock all cars.
Bonus song
At the “Press Start” screen, press Up, Down, Up, Down, A, B, X, Y to unlock a bonus song for Romones Style.
The image featured at the top of this post is ©The Legend of Heroes: Trails of Cold Steel III key art / Original