Kaiju No. 8

Kaiju No. 8 (Japanese: 怪獣8号, Hepburn: Kaijū Hachigō), also known in English as Monster #8, is a Japanese web manga series written and illustrated by Naoya Matsumoto. It was serialized on Shueisha's Shōnen Jump+ app and website from July 2020 to July 2025, with its chapters collected in 16 tankōbon volumes. Shueisha has also published the series digitally on its Manga Plus platform in English and several other languages. Viz Media began publishing the series digitally in August 2020 and has published the series in print in North America since December 2021.

The story follows Kafka Hibino who, after ingesting a parasitic creature, gains the ability to turn into a kaiju and now must navigate using his power while trying to become part of an organization that eliminates kaiju to fulfill a promise he made with a childhood friend. Matsumoto wrote the outline of the story of Kaiju No. 8 near the end of 2018 making it his second series for the magazine. The series was heavily influenced by Japanese tokusatsu media, especially Ultraman, while the author's struggles in the manga industry served as a basis for the main character's backstory.

An anime television series adaptation produced by Production I.G aired from April to June 2024, with a second season aired from July to September 2025. A "conclusion arc" to the anime series has been announced. The series has spawned a light novel, two spin-off manga series, and a video game.

By September 2025, the manga had over 19 million copies in circulation. The series has been praised for its premise, characters, and art. The series won the Next Manga Award in the web manga category in 2021 and was nominated for the Eisner Award in 2022.