In a world where black portals known as "Dungeons" suddenly appeared out of nowhere bringing a series of "Monster Waves", Just a few humans received the power to fight them and obtained the title of "Hunters". In South Korea due to the precarious situation they are currently living in, the government decided to proclaim a new law where if a member of the family with the ability of a "Hunter" joined the army and served to fight the Dungeons for 10 years, the rest of their siblings will be exempted from military service; Because of this a trend between wealthy families started to rise where they would adopt a child with the sole purpose to send them to the military service and exempt their real children. Yeonwoo our protagonist was adopted for this same motive, he lived most of his life with the purpose to be a tool to protect his "younger sibling" Jongwoo. He succeeds in joining the army but when a new dungeon appears near the place where Jongwoo lives, he jumps forward and volunteers to go and help contain the next monster wave. However after fighting for saving his life and reuniting again, the awkward tension and past mistakes will rise again between these two. Yeonwoo's only goal was always to protect Jongwoo so, how much is he willing to sacrifice for him?