"Zeroin" is a manga series that centers on a dystopian world where humanity is on the brink of extinction due to a catastrophic event known as the "Collapse." This event has left the planet ravaged, with most of the population wiped out and the remaining survivors struggling to rebuild society. The story primarily follows a group of individuals who are part of a specialized unit tasked with combating the mysterious entities known as "Nulls," which emerged after the Collapse. These Nulls are hostile, otherworldly beings that threaten the fragile remnants of human civilization.

The protagonist, a young man named Kaito, is a skilled fighter who joins the unit after losing his family to the Nulls. Kaito is driven by a deep desire for revenge and a determination to protect what little remains of humanity. Alongside him are other key members of the unit, each with their own motivations and backstories. These include Rina, a tactical genius with a calm demeanor, and Haruto, a former scientist who harbors guilt over his role in the events leading up to the Collapse. Together, they form a cohesive team, relying on their unique skills and shared resolve to face the relentless threat of the Nulls.

As the story progresses, the unit uncovers unsettling truths about the origins of the Nulls and the true nature of the Collapse. It becomes apparent that the catastrophe was not a random event but the result of human experimentation gone awry. The group must navigate a web of conspiracies, betrayals, and moral dilemmas as they fight to survive and uncover the secrets of their world. The narrative explores themes of survival, sacrifice, and the consequences of unchecked ambition, all while maintaining a tense and action-driven pace.

The manga balances intense combat sequences with moments of character development, delving into the personal struggles and relationships of the main cast. Kaito's journey from a vengeful loner to a leader who values his comrades is a central arc, while the supporting characters each undergo their own growth, adding depth to the story. The world-building is detailed, with a focus on the bleak, post-apocalyptic setting and the technological remnants of the old world that both aid and hinder the survivors.

"Zeroin" is a gripping tale of resilience in the face of overwhelming odds, blending science fiction, action, and emotional storytelling. The series keeps readers engaged with its intricate plot, well-developed characters, and the constant tension of a world teetering on the edge of annihilation.