Kamen Rider: The Bike Race Codes -

Kuuga:
Successfully complete the game.

Agito:
Successfully complete the game two times.

Kamen Rider 1 alternate:
Unlock Agito, then successfully complete the game again. Highlight Kamen Rider 1 at the character selection screen and hold L1 + R1 for an alternate costume.

Kamen Rider 2 alternate:
Unlock Kamen Rider 1 alternate, then successfully complete the game again. Highlight Kamen Rider 2 at the character selection screen and hold L1 + R1 for an alternate costume.