The events of the anime series "Kekkai Sensen" take place in the distant future. A mysterious portal to a parallel dimension opens in the sky above New York, and terrifying creatures such as monsters, beasts, and unseen animals begin to emerge onto Earth. The population is evacuated, and the metropolis ceases to exist. In its place, the town of Hellsalem is formed, where people who chose not to leave coexist with guests from another world. The border of the settlement is guarded by a squad from the secret organization "Libra."