Thirty years ago, the sudden emergence of unknown invasive alien lifeforms nearly led to the end of the world. Since then, humanity and these creatures, known as Invasion Species, have continued to clash over territory. While human safety is barely maintained, the world teeters on the edge of collapse. As the threat of death and destruction looms, people go about their daily lives, ignoring the constant danger. In response, the United Nations establishes EXCEEDS, an organization dedicated to investigating and combating threats posed by the Invasion Species. The story begins in the Far Eastern island nation of Mizuho, where Shiina Kuze, a young hunter who exterminates invasive species, lives on a remote island. Longing for a quiet life with her only family—her younger sister, Setsuna—Shiina's routine is disrupted when an unexpected incident occurs, pulling her into a much larger conflict.