"Kekkai Sensen," also known as "Blood Blockade Battlefront," is set in a fictional version of New York City called Hellsalem's Lot, which has been transformed into a chaotic melting pot of humans and supernatural beings after a sudden rupture between Earth and the Beyond. The city is sealed off from the outside world, and its inhabitants must navigate a precarious coexistence between the two realms. The story centers on Libra, a secret organization tasked with maintaining order and preventing catastrophic conflicts between humans and the otherworldly entities that now inhabit the city.

The protagonist, Leonardo Watch, is a young photographer who gains the "All-Seeing Eyes of the Gods" after a mysterious incident involving his sister, who loses her sight in exchange. Drawn to Hellsalem's Lot in search of answers and a way to restore his sister's vision, Leonardo becomes entangled with Libra. Despite his lack of combat experience, his unique ability to see through illusions and perceive hidden truths makes him a valuable asset to the organization.

Libra is composed of a diverse and eccentric group of individuals, each with their own supernatural abilities and quirks. Notable members include Zapp Renfro, a brash and hot-headed swordsman; Chain Sumeragi, a stoic and efficient werewolf-like investigator; Klaus von Reinherz, the noble and imposing leader of Libra; and Steven A. Starphase, a calm and calculating strategist with ice-based powers. Together, they tackle threats ranging from rogue supernatural entities to criminal organizations, often with a mix of humor, action, and unexpected camaraderie.

The narrative unfolds through episodic adventures that highlight the team's missions and the challenges of living in a city where chaos is the norm. Amidst the action, the series explores themes of coexistence, identity, and the blurred lines between good and evil. Leonardo's personal journey to understand his powers and protect his sister serves as an emotional anchor, while the larger story delves into the mysteries of Hellsalem's Lot and the forces that seek to exploit its unique conditions.

The series balances its high-stakes action with moments of levity and character-driven storytelling, creating a dynamic and engaging narrative. The interplay between the members of Libra, their individual backstories, and the evolving threats they face contribute to a rich and immersive world. "Kekkai Sensen" stands out for its inventive setting, vibrant characters, and seamless blend of supernatural intrigue and urban chaos.