For the last 80 year, the Titans have been all that matters. Thunderjaw were our response to their invasion, they are the pinnacle of our war machines, designed to be a match for the Titans. Our victories allowed humanity to live some good decades since, but in our hubris we've allowed ourselves to let our guard down, believing to be invincible. Now, the whole Earth is shaking again. The oceans part for another ascention, a final ascention with Titans larger than we've ever faced before coming to wipe us out. We can only hope that the Thunderjaw we have will be strong enough to take them down.