I used to think Phantom Pain was the full game, and GZ was the 'tanker' for lack of a better term, now I think the opposite. They're called Moby Dick studios, and there's a whale in the trailer, the whale is Moby Dick, the thing that took Big Boss's arm. Presumably it's just a fever dream metaphor for something that's happened to Big Boss, maybe it's someone taking Metal Gear, and now he has to hunt it. Could be anything really, but given the abstract aspects of PP, I think it's the smaller part of the game, because it's not literally happening.