This trophy is obtained simply by killing one enemy with each weapon in the game. Most of the weapons will be in your inventory and all you'll have to do is get a kill with them. That being said, there are some weapons that you'll have to pick up from enemies. Below is a list of weapons, what chapter they are found in at the earliest point, and how to obtain them.

Chapter 1

• C-78 Autoloading Pistol: Placed in inventory. You'll get your first kill in the game with this weapon.
• MK Service Revolver: Very Frequently dropped by enemies, you'll have to pick one up and get a kill with it.
• M2 "Falchion" Auto-Rifle: Placed in inventory. This will be the first rifle you'll get your hands on.

Chapter 3

• Duelist Revolver: Placed in inventory during your first enemy encounter of the chapter.
• M82 Selfloader Carbine: The first two guys you kill drop this weapon.
• M85 Automatisch: After killing the first two enemies, this gun is in the next room. After this point, enemies will drop this weapon every now and then.
• MK IV Grenade: You first start encountering these at these point, and they are present through the rest of the game.
• M84 Marksman Carbine: A sniper rifle that is found by killing the snipers firing at you in the windows near the beginning of the chapter. You can also find this weapon in the next immediate area in the room that provides a good overlook at the many enemies below you, the weapon is on the left side of the room if you face out the windows.
• RA-5 Repeating Shotgun: You'll know when you encounter an enemy with a shotgun, your ally will usually shout "shotgunner!" and that type of enemy will usually rush you with his shotgun. Once you kill this enemy, pick up the shotgun and get a kill with it.
• M86 Thermite Rifle: You'll have access to this weapon towards the end of this chapter, if you want to know all about this weapon, take a look at the  Up in Flames trophy.

Chapter 5

• C-81 Maschinenpistole: After you finish the sniping sequence in the ballroom, this gun is sitting on the table to your right. Additionally, it is dropped by some enemies in this chapter.
• Three Crown Coach Gun: This is a shotgun that is dropped by enemies, check enemies' dead bodies for this weapon when you get to the kitchen section.

Chapter 8

• T-23 Arc Induction Lance: This is the "electricity gun", and it is placed in your inventory at the start of the chapter.
• M4 Dragoon Revolver: Placed in inventory at the start of the chapter.
• TS-29 Cannon: Placed in inventory later in the chapter.

Chapter 9

• TS-17 Detonator: When you reach the docks you will climb to the top of a ship that is under construction. There will be an enemy with a grenade launcher there at the top that you will need to kill, pick up this weapon after you've killed him and fire rounds on the enemies below. 

Chapter 11

• Repeating Arbalest: Placed in your inventory at the beginning of the chapter, it's a crossbow-like weapon.