When the world of Eroa is inducted into the System without warning, Marcus Grey has the (mis)fortune of being the first person to 'opt-in', gaining a Superior Class. Rather than taking the fight to the monsters and dungeons that have come to populate his world, Marcus has become first in the line of defence as he struggles to maintain a balance between keeping others safe while not limiting their progression.

Together with his familiar Alice, Marcus works to build up his fortifications while avoiding the plots and greed of those who wish to take what is his.