Main Gauches

Main Gauches are daggers. They inflict +50% damage to enemies with the Vulnerable status when wielded by Noctis or Ignis.

Source
Main Gauches are given to Ignis in Chapter 14. They can later be purchased from the Culless Munitions in Hammerhead for 8,000 gil. They can be sold back to shops for 4,000 gil.