I'll try to be brief because the series hasn't been translated past the first four chapters.
After the initial group of Tsuyoshi, Kukuri, Shiori, Masaru, Etsuko, and Inaho escape the tunnel, they run into a camera crew hoping to film the ongoings of the abandoned tunnel. Both groups team up until they find a family of athletes in the mountain attacked by the insects.
However, Masaru, most of the camera crew, and the athletes' parents die of giant insects.
Going deeper into the mountain in search of an escape route, the survivors encounter a gang of criminals and a lone hunter. Working together, they manage to defeat the criminals and evade the giant insects, escaping the mountain. Plus, Tsuyoshi and Kukuri tie the not. However, the final chapter ends on a dark note, as the giant insects move toward the town below the mountain looking for food.