Gain S ranking
To gain the secret S ranking, score over 40,000 points in Street Work mode.

Unlock Secret Characters
The game's four hidden characters are unlocked the following way:

Complete all tracks in the Street Work mode with an A ranking
Clear all courses in the Time Attack mode within the time limit
Get a perfect rating in every track in the Coin mode
Complete all courses in the Street Work mode with an S ranking

Bonus boards
Unlock all four bonus characters. Then press Up (x2), Down (x2), Left, Right, Left, Right, B, A at the board selection screen to unlock the J-Arm, J-B, Ika-Chu and Father bonus boards.