The world is not as peaceful as it use to be. The gate of hell have been open and monster start to poured out from the gate. Scarlett Drachen code name 'The Slayer'. Never leave anything alive when she done with the mission. She only work alone and that's her style. No one really know how 'The Slayer' looks like because in their eyes Scarlett is a nobody that got lucky with the entrance exam and a failure. She didn't like to interact with other and no one has saw her taking any mission. They all thought that 'The Slayer' is a man,never a 19 years old girl. She is one of the agents in 'Black Op'. This agency is place where there a chance for you to lose your life if you messed up the mission. This agency keep monsters from destroying the world. But suddenly she was asked...no...more likely being order to be in a team that have 5 boys and being their teammate. What will happen with Scarlett's live when she have to live under the same roof as those boys? Will Scarlett told them about her codename?