怪獣大国日本。清掃業で働く日比野カフカは、日本防衛隊のホープである幼馴染・亜白ミナとの再会をきっかけに諦めていた防衛隊を再び志すが、その矢先に強大な力を持つ「怪獣８号」に変身してしまう。後輩・市川レノの協力を得て正体を隠しながら、防衛隊員選抜試験、初の実戦と、かつての夢へ着実に歩みを進めるカフカ。しかし日常を揺るがすように、高い知能を持つ謎の怪獣によって防衛隊基地の襲撃事件が発生！絶望的な状況を前にカフカはある重大な決断を迫られる…。
In a Kaiju-filled Japan, Kafka Hibino works in monster disposal. After reuniting with his childhood friend Mina Ashiro, a rising star in the anti-Kaiju Defense Force, he decides to pursue his abandoned dream of joining the Force... when he suddenly transforms into the powerful "Kaiju No. 8." With help from his junior colleague Reno Ichikawa, Kafka hides his identity while striving towards his life-long dream of passing the Defense Force exam and standing at Mina's side. But when a mysterious intelligent Kaiju attacks a Defense Force base, Kafka faces a crucial decision in a desperate situation...
