From the introduction: Welcome back to Earth, jumper! No, you didn’t head home just yet, but this world is remarkably similar to your own, at least before the Dungeon Shock. In 2012, every subway station around the world overflowed with monsters, and in their place, portals were formed. Through each portal, a copy of the original subway station could be found, with monsters located within. If the dungeons aren’t cleared by killing the monsters within and getting the Return Stone to deactivate the barrier and leave, after 30 days the monsters will break out and likely destroy the surrounding areas before they can be put down. Fortunately, a new type of hero emerged. The Roused are those who have awakened abilities similar to RPG characters, and are considered the only people capable of clearing dungeons. This, combined with the mysterious Bloodstones found within monsters that can be used as an energy source, means that humanity can put up a good fight against the monsters. In five years, a mysterious man name Kang Woojin will return from another world and attempt to clean up the world himself.