Kekkai Sensen Back 2 Back centers around the crime fighting organization "Libra" and their battles in Jerusalem's Lot, formerly known as New York City. Jerusalem's Lot was created in a single night when a portal to the "Beyond" opened, and now it is a paranormal melting pot of monsters, magic, and the everyday mundane city life. It's up to Libra to prevent the horrors of this city from spreading to the outside world.