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 a new coworker Reno Ichikawa, while cleaning up Kaiju remains, whose 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.