The Thunder Cage is one of the most accessible Ultimate weapons to farm in The First Descendant. You get all the crafting materials as early as the 2nd region, Sterile Land, and you might have been lucky to get some materials while going through the campaign. It is a fast-firing submachine gun, which makes it popular for close-range builds and those who want to be fast.
It is a top-tier weapon, and here’s the best Thunder Cage build in The First Descendant you can follow, complete with modules, readjusted stat rolls, and more.