Regarding the Sole Successor

One day, “Holes,” from which monsters emerge, appeared in the world. Those who can close these holes are called “Guards.” “Please save me. Please…” On the day I desperately wished for it, I became a “Guard.” However… The color of my system window is different. I cannot see the system’s inherent domain. The system’s skills are strange. This is the story of a “unique,” a “sole” Guard, different from others.