You play as a pair of giant robot pilots who together control their giant robot as one. Your immediate thought is Pacific Rim, right? Partly because of the title, but also because it sounds similar as it was recently released as a film. In actuality this is more like Jinki: Extend or Jinki, as I’ve only seen Extend I couldn’t say.
One of you controls the upper body movement via control-less interface, such as Kinect. The other controls the leg movement, transformation control, etc. via a standard controller, such as a gamepad or keyboard and mouse. This asymmetric gameplay allows two players to work together in very different ways, which I think is pretty cool.
As with a lot of mecha, the storyline isn’t that important. Giant freaking robots, right?