"Kujira no Kora wa Sajō ni Utau" (Children of the Whales) is set in a world covered by vast seas of sand, where a group of people known as the Mud Whale live aboard a massive, floating island-like vessel. The inhabitants of the Mud Whale are divided into two groups: the Marked, who possess supernatural abilities called thymia but have short lifespans, and the Unmarked, who lack powers but live longer lives. The society is isolated, with no contact with the outside world, and is governed by a council of elders.

The story centers on Chakuro, a young archivist who records the history of the Mud Whale. Chakuro is one of the Marked and is deeply curious about the world beyond the sand sea. During an expedition to investigate a mysterious island, Chakuro and his companions encounter a young girl named Lykos, who is from the outside world. Her arrival disrupts the fragile balance of the Mud Whale’s society, revealing that their isolation is not accidental but enforced by external forces.

As Chakuro and Lykos grow closer, they uncover dark truths about the Mud Whale’s origins and the broader world. The Mud Whale’s existence is tied to a larger conflict involving an empire that seeks to control the Marked and exploit their powers. The empire views the Mud Whale’s inhabitants as dangerous and seeks to eliminate them. The story explores themes of survival, identity, and the consequences of power as the characters grapple with their roles in a world that seeks to destroy them.

Key characters include Ouni, a rebellious and powerful Marked individual who challenges the elders’ authority; Suou, the young and inexperienced leader of the Mud Whale; and Sami, Chakuro’s close friend who struggles with the limitations of her short life. The narrative delves into their personal struggles and relationships while building tension as the Mud Whale’s society faces increasing threats from both within and outside.

The series combines elements of fantasy, dystopia, and political intrigue, creating a layered story that examines the cost of freedom and the weight of inherited legacies. The characters’ journey is marked by loss, discovery, and the pursuit of a future where they can define their own destinies.