There are 17 weapons that you can collect, but only 16 of them are required for the trophy (and the 100%). The shield doesn't count. Most of these weapons can be found during the story or side quests.
List of the required weapons :
- Stick
- Crossbow
- Sword
- Scythe
- Axe
- Halberd
- Horse Shit
- Luth
- Auto Crossbow
- Spear
- Pickaxe
- Hand
- Rock
- Excalibur
- Holy Hand Grenade
- Jousting Lance