After the invading dimensional monsters were beaten back, Seoul was rebuilt. This is the story of Closers in New Seoul.
Mysterious dimensional gates opened all over the planet and unleashed a worldwide invasion of dimensional monsters. No monsters and tactics had any effect on the waves of dimensional monsters pouring out of the dimensional gates. City after city was mercilessly destroyed.

But the opening of the dimensional gates did not only cause damage and destruction. The psychokinetic power that it awoke also enabled a tiny minority of humans to gain extraordinary psychic powers. With these psychic warriors, governments around the world were able to turn the tide of the war with these monsters. After unspeakable losses, the people of earth at least succeeded in closing the gates. Since they had closed the gates, these psychics began to be called "CLOSERS," and the invasion of the dimensional monsters was named the First Dimensional War.

With the dimensional monsters vanquished, peace returned to the world, and the cities were rebuilt. Through dedicated research into the dimensional gates and psychokinetic power, humans learned that the gates open when there is a singularity in this mysterious power. However, their understanding of the gates was still incomplete. The CLOSERS who survived the First Dimensional War became part of an organization called UNION. Together, they researched the psychokinetic power in all over the world, working to prevent another dimensional war.

And that's when the dimensional gates all over the world started shaking again - as ever stronger outbreed creatures renewed the attack on earth.

[Source: Wikipedia]