The story of Armored Core 4/FA is pretty halfway done, but if you keep an close eye out it starts to make sense. The last guy in Armored core 4 you fight is Joshua O'Brian, the owner of White Glint in 4. In For Answer the YOU in 4 is the pilot in For Answer's White Glint the " Ghost of Rayoleonard" (which is the company you worked for in the last game that died) So you're basically fighting you lol.
I would have spoiler posted this in the forums, but I'm not quite sure how to use spoiler text yet.
