A Better Pair of Plunderers - Hammerhead
First Available: Chapter 8
Other Requirements: Complete Living Off The Land & Acquire Plunderers
Rewards: 800 EXP & Plunderers II
You're able to accept this quest after obtaining the Plunderers item which you get for trading Caem Carrots to Tony. In order to obtain these carrots you'll first need to complete the side quest Living off the Land during Chapter 8. Select the "weapons" option at Tony and you'll receive either the Plunderers, Force Stealer, Valiant or an Absorb Shield, which are all other items that you can upgrade at Cid.
In order to upgrade the Plunderers you'll need to obtain a Barbed Scythe item which drops from Soldier Wasps in Malmalam Thicket. If you've already been to this dungeon chances are you have this item, otherwise just head over to the dungeon and clear it - the item is pretty common. A picture of the enemy you're looking for is below.