In Soul Calibur 5 for the PS3 and Xbox 360, you can unlock Legendary Souls mode, which is basically a boss rush type mode. You’ll fight boss after boss, so this can be a challenging mode if you’re looking for a good fight.
To unlock Legendary Souls mode, you just need to beat Story mode with any character.
Check out my other article for the full list of unlockables in Soul Calibur 5.