Kaiju No. 8 is a manga series set in a near-future Japan plagued by monstrous creatures known as kaiju. The story follows Kafka Hibino, who initially works as part of a cleanup crew responsible for disposing of the remains of defeated kaiju. Despite his dreams of becoming a member of the Japanese Defense Force, he has failed the necessary trials and feels stuck in his current role.

Kafka's life takes a dramatic turn when he accidentally ingests a small kaiju, granting him the ability to transform into a kaiju himself. This newfound power presents Kafka with a second chance to pursue his dream of joining the Defense Force, which is currently opening trials for new recruits. The narrative explores Kafka's struggles and adventures as he navigates his dual identity and the challenges of becoming a hero while dealing with the consequences of his transformation

The series combines elements of action, comedy, and personal growth, showcasing Kafka's journey from a mundane job to potentially becoming a key player in the fight against kaiju threats.