The First Descendant

This achievement has a pre-req of Mastery Rank 9. As mentioned in No Hope for the Vulgus (40G) you'll need to have two copies of the same Ultimate tier weapon for this achievement. You should have one Thunder Cage already, and once you hit MR9 you'll get a side-quest to speak to the training robot in Albion who will give you a second copy to perform this function. With your two Thunder Cage weapons on hand, go to a workbench, choose " Enhance Unique Ability" and then select the two weapons, pay a small fee of 50k gold, and voila, achievement unlocked!