You could try building the torso out of foam board, glue the sheets together to get the size and depth you need then start shaping it by cutting it away. Then when you are finished coat it with fiberglass resin and it should good...just a thought. It will be a lot of work though. If you had the money and the access to modeling software you could model the shape you want and then pay a machine shop to CNC the shape out of the foam (there is a special foam for that) and then you could coat it with fiberglass resin:)
I does look like a lot of work, the model plus the game will take forever and I've only got around 10 months to get this done. An alternative that I thought of would be purchasing an actual figure of the 3 diferent EVA from the anime and using the hardware to build Neo Tokyo (the city featured in the anime), then place the figures interacting with the hardware.
For example one smashed into the graphics card. . .that's the only one I thought of