Imagine Being a part of the scout regiment when two young boys (according to Ed, MEN) join. One was short with a blond hair, mechanical arm and leg. And the other with just a suit of armor and high pitched voice. After discovering a that you risk your lives to get to a basement with the secret and what might be information on the titans, they introduce Alchemy to you. They help create Transmutation  Circles in your 3d Maneuver gears to help you, Erin, Mikasa, and Armin Get to the basement. And who knows, maybe you'll just come across a Philosophers Stone.