In a world plagued by monstrous kaijuu, the Defense Corps valiantly battles to protect Japan. Kafka Hibino, a disillusioned sweeper longing to join the elite military unit, rekindles his ambition when he meets the determined recruit Leno Ichikawa. After a fateful encounter with a parasite-type kaijuu transforms him into a humanoid monster, Kafka seizes the opportunity to pursue his long-abandoned dream of becoming a kaijuu-fighting hero.