Kekkai Sensen focuses on the crime-fighting organization "Libra" and their conflicts in Hellsalem's Lot, formerly known as New York City. Hellsalem's Lot came into existence overnight when a portal to the "Beyond" opened, transforming it into a paranormal melting pot of monsters, magic, and ordinary city life. It falls to Libra to stop the city's horrors from spreading to the outside world. When mild-mannered Leonard Watch arrives in the city, he is inducted into Libra, and things spiral out of control from there.