Supersonic monkeys, vampires, talking fishmen, and various other supernatural monsters coexisting with humans—this has become a routine part of life in Hellsalem's Lot, formerly New York City, for quite some time. Three years ago, a gateway between Earth and the Beyond opened, trapping both New Yorkers and creatures from the other dimension inside an impenetrable bubble, forcing them to live together. Libra is a secret organization made up of eccentrics and superhumans, charged with maintaining order in the city and preventing chaos from spreading to the rest of the world. Leonardo Watch pursues photography as a hobby and lives a normal life with his parents and sister. However, after he acquires the "All-seeing Eyes of the Gods" at the cost of his sister's eyesight, he travels to Hellsalem's Lot to help her by seeking answers regarding the mysterious powers he has received. He soon encounters Libra, and when Leo unexpectedly joins their ranks, he finds himself in deeper trouble than anticipated. Kekkai Sensen follows Leo's misadventures in the strangest place on Earth alongside his equally bizarre comrades—as the ordinary boy unwittingly watches his life take a turn for the extraordinary.