This is a world where there are monsters called Shards. There are also gigantic alien Mech's that are sent from space to help humans fight the Shards. The people who pilot these Mech's are called Mech Cadets who train for years to be able to pilot a Mech. When a Mech comes in from space the Mech Cadets to a variety of tests such as fighting to test strength and do races to test speed. This all happens when the Mech's are observing them, after these tests the Mech's will choose who their pilots.