"Zetsumetsu Kigu-shun–" is a science fiction anime series set in a dystopian future where humanity faces extinction due to the emergence of mysterious, hostile entities known as "Kigu." These creatures, which resemble mechanical beasts, have driven humans to the brink of survival, forcing the remnants of civilization to take refuge in fortified cities. The story centers on a group of young individuals who are part of a specialized unit tasked with combating the Kigu and uncovering their origins.

The protagonist, a reserved yet determined teenager named Haruto, is thrust into the conflict after a personal tragedy involving the Kigu. Haruto joins the "Kigu-shun," an elite squad equipped with advanced exosuits designed to combat the mechanical threats. Alongside Haruto are several key characters, including Aoi, a tactical genius with a sharp wit; Ren, a hot-headed but fiercely loyal fighter; and Yuna, a skilled engineer who provides technical support and develops weapons to counter the Kigu. Together, they form a cohesive team, each contributing unique skills to their missions.

As the series progresses, the Kigu-shun uncovers unsettling truths about the Kigu's origins, revealing a connection to humanity's own technological advancements. The narrative explores themes of survival, sacrifice, and the ethical implications of artificial intelligence and human innovation. The team faces escalating challenges, both from the increasingly powerful Kigu and from internal conflicts within their own ranks, as differing ideologies and personal motivations come to the forefront.

The plot is driven by a series of high-stakes missions, interspersed with moments of character development and interpersonal dynamics. The series balances action-packed sequences with introspective moments, delving into the psychological toll of living in a world on the brink of collapse. As the Kigu-shun uncovers more about the Kigu, they are forced to confront difficult questions about humanity's role in its own downfall and the possibility of coexistence with the very entities threatening their existence. The story builds toward a climactic confrontation that tests the limits of the team's resolve and their understanding of the world they are fighting to save.