"Kuro no Su - Chronus" is a science fiction anime series set in a dystopian future where humanity is on the brink of extinction due to the emergence of mysterious entities known as "Chronus." These beings, which appear as shadowy, time-manipulating creatures, have disrupted the natural flow of time, causing catastrophic anomalies across the world. The story centers on a group of individuals who possess unique abilities tied to the manipulation of time, known as "Chronos Users," and their struggle to restore balance to the fractured timeline.

The protagonist, Ren Kurogane, is a young man who wields the power of "Chronos Break," an ability that allows him to freeze time for a brief period. Ren is initially reluctant to embrace his role as a Chronos User, but after witnessing the destruction caused by the Chronus and the loss of his loved ones, he joins a resistance organization called "Tempora." This group is dedicated to combating the Chronus and uncovering the truth behind their sudden appearance. Alongside Ren are other key characters, including Aya Fujisaki, a skilled strategist with the ability to rewind time in localized areas, and Kaito Shindou, a former soldier who can accelerate time within a limited radius.

As the series progresses, the narrative delves into the origins of the Chronus, revealing that they are not merely random anomalies but the result of a failed experiment conducted by a secretive organization known as "Epoch." Epoch sought to harness time itself as a weapon, but their experiments inadvertently created the Chronus, which now threaten to unravel reality. The characters must navigate a complex web of alliances and betrayals as they uncover the truth about Epoch's involvement and the true nature of their own powers.

The plot is driven by a series of high-stakes battles against increasingly powerful Chronus, as well as internal conflicts within Tempora. The series explores themes of sacrifice, the consequences of tampering with time, and the resilience of humanity in the face of overwhelming odds. The story builds toward a climactic confrontation between Ren and the leader of Epoch, who seeks to use the Chronus to rewrite history and create a new world order. The resolution of the series hinges on the characters' ability to reconcile their personal struggles with their duty to protect the timeline, culminating in a finale that ties together the narrative threads while leaving room for contemplation on the nature of time and destiny.