In a distant future, humanity resides in an underground fortress called Le Bastion Souterrain. The story follows Lucas Morel, an 18-year-old who works in the hydroponic gardens until he receives a conscription notice to join the military. As he prepares to leave his mother and visits his ailing grandmother, we get glimpses of life within the strictly controlled confines of this subterranean society.
Upon arriving at the Military Academy, Lucas and other young recruits are introduced to the impressive D-50 Exo Units - advanced mechanized suits that form neural connections with their pilots. As the recruits begin their training, they experience the stark contrast between their previous civilian lives and their new military roles.