In a world where dungeons have opened and some people awaken as hunters, South Korea offers an unusual deal—become a hunter and serve for ten years, and your siblings will be exempt from military service. This leads to a strange trend of wealthy families adopting children to shield their own. Yeon-woo was adopted under such circumstances, becoming a hunter to protect his younger brother, Jeong-woo. Now, five years into his service, when an unknown dungeon opens near Jeong-woo's university, Yeon-woo volunteers for a dangerous mission, ready to risk everything to protect his brother—even his life.