Each of the four main characters must fight their rival boss.

Unlockable	How to unlock
Alex Third Costume and 2nd Weapon	Must fight the last boss (Miguel).
Burns Third Costume and 2nd Weapon	Must fight Huge Red Robot (Gasshu Revived).
Michelle Third Costume and 2nd Weapon	Must fight the green punk ninja (Brennum) on the elevator.
Rachel Third Costume and 2nd Weapon	Must fight the woman with the claws (Cassandra).