The lastest 1.13 Title Update adds the long awaited Magitek Exosuit along with the quest titled 'O Partner, My Partner' given to the party by a hunter located at the Meldacio Hunter HQ near the Vesperpool on the north side of the map.
In the quest you face a lvl 99 monster called Melusine. With the new Exosuits she is a pushover as the suits grant you invicibility for 30 minutes, plenty of time to finish her off. Make use of the Zwill Crossblades and Armiger along with Gladio's Impulse, Prompto's Recoil and Ignis' Enhancement to make short work of her.
The achievement will unlock when you return to the hunter to turn in the quest.