For many years, Japan has been tormented by grotesque kaijuu - Godzilla-like creatures. The Defense Corps, an esteemed military unit, bravely defends civilians from these beasts day in and day out. When a kaijuu is defeated, the Professional Kaijuu Cleaner Corporation hires sweepers to clear their remains. Kafka Hibino, a 32-year-old sweeper, has always longed to join the Defense Corps and become a kaijuu slayer. Despite several attempts, he has been unsuccessful and has settled for a mundane yet profitable life. But when Leno Ichikawa, an ambitious teenage recruit, joins Kafka's cleaning team, his yearning for military service is reignited. Fate intervenes when Kafka encounters a parasitic kaijuu that enters his body forcibly, transforming him into a humanoid creature with enhanced abilities. With this newfound strength, Kafka decides to take a chance and pursue his lifelong dream.