Nine years after extraterrestrials saved Earth from an asteroid collision and were welcomed as heroes, they now live alongside humans in Japan, enjoying a privileged and untouchable status. Society celebrates them, but this harmony masks a deep-seated resentment felt by those who see the aliens as arrogant overlords who look down on humanity. In this tense environment, Nomamoto, a factory worker trapped in a dead-end job with an abusive alien boss, struggles with her simmering hatred for the beings she blames for her misery.

Nomamoto's life changes when she meets Kitami, a new coworker whose family was murdered by aliens. Their shared anger forges a dark friendship, but Kitami takes their mission to an extreme, committing an unthinkable act by killing an alien and bringing the body to Nomamoto. This event plunges them into a violent conspiracy, with Kitami murdering aliens while Nomamoto disposes of the bodies in a shocking manner, consuming them because she finds them delicious. The two outcasts become radicalized, positioning themselves against both the alien population and the human society that worships them.

The narrative expands beyond their initial revenge spree when a mysterious alien named Lily enters the story. Lily, who is connected to the tragedy that destroyed Kitami's family, becomes an unlikely ally, helping him kill other aliens and even saving his life. This alliance forces Kitami to confront the rigid us versus them logic of his crusade, especially after he discovers that the true killer was not Lily but her twin brother Lally. A subsequent story arc delves into Lally's past, portraying him not as a monstrous killer but as a young alien boy who was bullied and isolated at school, having been in love with Kitami's sister before the fatal incident. This revelation complicates the narrative's morality, showing how prejudice, social privilege, and the protection of a dominant class can perpetuate cycles of violence from all sides. As the series progresses, characters like Backbone join the pair in their missions, and the story continues to explore themes of systemic injustice, trauma, and the ugly reality of becoming a monster to fight monsters.