The story revolves around Kafka Hibino, a 32-year-old longing to join The Defense Force and make good on his promise to a childhood friend, Mina Ashiro. He befriends Reno Ichikawa, a new coworker, while cleaning up Kaiju remains. Reno’s determination to join The Defense Force inspires Kafka to fulfill his childhood promise to pass the entrance exam and join Mina to protect humanity. When a small Kaiju burrows itself inside Kafka, he gains superhuman strength and powers fit for fighting Kaiju. He works to earn the trust of his human teammates, defeat increasingly powerful Kaiju, and keep the world safe. Part human and part Kaiju, Kafka recognizes the creature beginning to take over more frequently, and he must fight to hold on to what makes him human.