Everything Cain Igarashi thought he knew is upended as he finds himself ripped from Earth and summoned to the besieged world of Ranael by a mysterious group known as Last Bastion. This strange world is under attack by otherworldly creatures from beyond the stars, called the Bottomless. This “Last Bastion” that summoned Cain seems to be a resistance force fighting against the Bottomless and trying to save the world. They used a ritual to try to bring forth a being capable of saving Ranael, but it doesn't seem like Cain is quite what they were looking for.

Cain struggles to adapt to the life of constant conflict that comes with being part of Last Bastion, leading him to wonder: Can he even belong here? As Cain navigates through new friendships, challenges, wonders, and an odd affliction, he realizes he has a choice to make. Does he simply accept his place in this new world and try to survive? Or does he try to become the catalyst of change that this broken world so desperately needs?