This is a future cosplay that repurposes previously crafted personal creations. The Parahunters were a proposed faction for the game of “Fallout 4”, but they never made it past the concept phase. They were basically designed as a rival faction to the Brotherhood of Steel, acting as mercenaries and poachers of mutated beasts in the Wasteland. This particular armor was probably found mostly intact by a wandering Vault Survivor after the Great War, its original pilot long since dead due to radiation exposure.
‘Fallout’ and its related properties are owned by Bethesda. I lay claim to nothing; this is simply intended as an homage.
EDIT: I have since added a light mini-Gatling gun to the left shoulder pauldron. It literally snaps into place and is painted and detailed to match. I imagine it could fire something like 7 mm caseless light armor piercing rounds.