Jeju Island S-Rank Gate

The Jeju Island S-Rank Gate is the gate that costs Korea an entire island in Solo Leveling, opening on Jeju about four years before the main story begins. The Korean Hunters Association launches a search and destroy mission to clear it and the mission fails, which leaves the gate to run its seven-day clock down to a dungeon break. The ant magic beasts inside cross into the human world, and the island is written off as unfit to live on. Two more search and destroy missions over the next two years achieve nothing either, and after the third failure the government stops trying, on the reasoning that the colony will starve once the island runs out of food. The ants do not starve. They adapt, growing wings that carry them to the islands nearby.