The gate spawned on Jeju Island about four years before the events of the main storyline. Due to how weak the Korean S-Rank Hunters were at the time, they failed to close the gate and it eventually underwent a dungeon break, resulting in the deaths of thousands of Korean civilians and turning the island into a wasteland no longer fit for human habitation.

Over the next three years, the Korean government launched three search-and-destroy missions on the island to no success. When the third raid resulted in the death of Eunseok, one of their prized S-Rank Hunters, the Korean government formally abandoned their efforts to reclaim Jeju and decided to leave the island alone in hopes that the ants would eventually perish on their own by starving to death when their food supply eventually ran out. Unfortunately, this move backfired, as the ants eventually started evolve and develop wings that enabled them to fly over long distances.

In response to this evolution, the Draw Sword Guild, Japan's strongest and largest guild, agreed to collaborate with the Koreans in liberating the island before all of the ants learned how to take flight. A simple but promising plan was worked out; the Japanese S-Rank Hunters would use themselves as bait to draw out the ants, while the Korean S-Rank Hunters would sneak into the unguarded nest and kill the queen. Thus they formed Jeju Island Raid Party which consisted of sixteen S-Rank Hunters.

Initially, the raid went well, with the Japanese easily slaughtering the ants and the Koreans killing the queen and her guards with minimal trouble. However, the situation took a horrible turn when an incredibly powerful ant called the Ant King.

the S rank hunters were injured heavily. And since Byung-gu was dead now, they didn’t had any healers, causing them to weaken. Baek was being choked by the Ant King currently, the claw scars on Baek’s chest were not helping honestly.

a small help would’ve been nice, wouldn’t it?