In the year 2206, Earth is on the brink of destruction. Widespread pollution and severe resource shortages have led scientists to conclude that the planet will become uninhabitable within the next hundred years. In a desperate attempt to ensure humanity's long-term survival, the world's remaining governments place their faith in Gaia, a powerful artificial intelligence. Gaia concludes that the human population must be drastically reduced, and to do so, it initiates a deadly tournament. Sixteen surviving nations each select a young delegate, boys and girls who possess extraordinary abilities, to compete in the Nation Extinction Tournament. The stakes are absolute: the winning nation gains the right to completely exterminate the citizens of one losing nation of its choice and seize its strategic assets. For the delegates, to win is to become a hero, but to lose means death not only for themselves but for everyone in their homeland.

The central figure of the story is Hasuichi Nishizono, the son of Japan's Prime Minister, who is chosen as his nation's delegate. His first opponent in the tournament is the representative from the United Kingdom, a violent serial killer named Albie Hiddleston. The fighters are a new breed of human, enhanced by what are known as Theseus Cells, which allow them to adapt and shapeshift in real-time during combat, achieving higher levels of power and "resonance". Despite the brutal reality of the tournament, Hasuichi clings to a seemingly impossible idealistic goal: he wants to win the competition without allowing anyone to die, a naive hope that stands in stark contrast to the tournament's genocidal rules.

As the first match between Japan and the United Kingdom unfolds, the narrative delves deeper than the surface-level action. The motivations of the AI, Gaia, come into question, hinting that its true goals may be more complex than simply saving humanity. Flashbacks explore the past of characters like Albie, revealing a tragic history with a woman named Rose that shaped his brutal worldview and his belief that tomorrow is never guaranteed. Similarly, Hasuichi's own resolve is shown to be rooted in poignant childhood memories of his sick mother. The series thus balances its gritty, violent tournament battles with political maneuvering among the world's leaders and philosophical questions about survival, sacrifice, and the nature of humanity when pushed to its limits. Serialized in Monthly Comic Zenon, the manga presents a pre-apocalyptic sci-fi world influenced by classic genre works, setting the stage for a conflict where the fate of entire nations rests on the shoulders of a few young fighters.