The Kaiju Wars have just begun...

KAIJU No. 8

Kaiju No. 8 is set in a world in which monsters named kaiju regularly cause disasters. Japan is the country with the highest rate of kaiju attacks in the world and, to combat them, it establishes the Anti-Kaiju Defense Force (日本防衛隊, Nihon bōei-tai, lit. "Japanese Defense Force"). Kaiju are assigned a “fortitude level” – a scale indicating their overall strength, and are classified as honju – more dangerous, stronger kaiju and yoju – smaller kaiju that can accompany or sprout off from the honju. Kaiju that have high fortitude levels or abnormal characteristics are given a number as an identifier based on when they first appear and are classified as daikaiju. Defense Force officers wear power suits made from kaiju remains that grant them increased strength, speed and durability. The suits have a total power output measured in the form of a percentage (referred to as "unleashed combat power") which vary from person to person depending on their ability with a maximum of 100%. The Defense Force consists of general officers and platoon leaders, with varying levels of unleashed combat power, and captains and vice-captains whose combat power exceeds 90% and who lead divisions. Daikaiju remains are used to create stronger weapons named Numbers (ナンバーズ, Nanbāzu) that some individuals can use if they are deemed compatible and that are named after the daikaiju they are made from.

After their town is destroyed by kaiju, childhood friends Kafka Hibino and Mina Ashiro both vow to become members of the Defense Force to fight kaiju together. Mina, now 27, has since become the captain of the Defense Force's Third Division while Kafka, now 32, has failed the examination numerous times and works as a member of a clean-up crew that dispose of kaiju remains after battle. Kafka meets a young part-time worker in his company, Reno Ichikawa, an aspiring Defense Force member, who reignites his desire to become part of the Defense Force. However, a small kaiju enters Kafka's body through his mouth and he gains the ability to turn into a kaiju. After escaping from the Defense Force, Kafka is given the code name "Kaiju No. 8" and decides to apply while keeping his kaiju form a secret.

Kafka and Reno are able to pass the examination and are inducted into the Third Division together with Kikoru Shinomiya, a kaiju-slaying prodigy, who finds out about Kafka's condition after he saves her from a humanoid kaiju, later named "Kaiju No. 9," who becomes their primary adversary. While fighting off an attack orchestrated by Kaiju No. 10, a daikaiju created by No. 9, Kafka reveals his kaiju form when he transforms to save the Third Division base from being destroyed and is, reluctantly, apprehended by Mina and taken into custody to be disposed of. While imprisoned, Kafka is tested in battle by the Director General of the Defense Force, Isao Shinomiya, who uses the Numbers 2 weapon made from the remains of Kaiju No. 2. Kafka survives the battle proving that he can control himself while transformed and avoids being disposed of. Kafka is transferred, along with Kikoru, to the First Division led by captain Gen Narumi where they are tasked to prevent another attack planned by No. 9. Kafka, Kikoru and Gen succeed in defeating two versions of No. 9 which are revealed to be decoys. The real one attacks Isao and absorbs him and his Numbers 2 weapon after which No. 9 becomes stronger and prepares for an invasion of Japan with new kaiju.