Defeat Centurion.

Defeat an enemy with a critical-hit headshot.

Attack an enemy to save your partner who is grappling with that enemy.

Finish the game on Normal difficulty or higher.

Finish the game saving Chris and Barry using Jill.

Save Chris from confinement using Jill.

Save Barry from Lisa Trevor.

Obtain the Helmet Key using Jill.

Save Jill using Barry.

Finish the game on Very Easy difficulty or higher.

Save Jill from confinement using Chris.

Defeat Black Tiger.

Obtain the "Last Book Vol. 2" using Chris.