Unlock Bunta's Subaru Impreza
Defeat Bunta during story mode with at least a "B" rank to unlock his Impreza WRX STi Version V at the Subaru section.
Obtaining Introductory Videos to All Cars
Complete the story mode with ranks B or above in order to unlock the introductory videos for all the cars in the game.
Race Against Bunta
Successfully complete Story Mode defeating Ryosuke to unlock Bunta as an opponent in Versus Mode.
Unlock Bunta in Arcade Mode
After you've beaten everyone in Arcade Mode, you will unlock Takumi Fujiwara on Irohazaka Downhill. After you've beaten him, you will unlock more racers and maps. After you've beaten everyone, you will unlock the last boss Bunta Fujiwara on Akina Downhill.
Extra Racers and Stages in Arcade Mode
Play arcade mode and beat every single character. After doing so, Takumi will be unlocked for you to race against in Happogahara. Beat Takumi, and you will unlock 5 extra courses in which you re-race certain opponents (i.e. Skyline, Sleighty, etc.) in their story mode courses instead of their lower difficulty levels from before.
Unlock Bunta's car, the GC8V
To unlock Bunta's car for use in Arcade or Time Attack mode, defeat Bunta in Story Mode (Stage 31). After beating him, the GC8V will be available in car manufacturer section under Subaru. By the way, this car only has one default tune option, and it only comes in one color.