To enchant your Laguna Weapon, you must go to @go quest and talk to the NPC. You will be able to add an extra effect or an element to your weapon. However, these additions will be generated randomly, so you won't be able to choose the one you want.
Talk to the NPC, and he will tell you that you can register, add an effect, and an element.
When you choose to Register a Laguna Weapon, it will check your equipment to see if you have any Laguna weapons. (The weapon must be equipped; it does not count if it's in your inventory).
Then it will ask you for the following things.
|Laguna weapon you want to enchant.||